RESEARCH & DEVELOPMENT
REPORT NO. RD 2047
APPLICATION OF HYDROELECTRIC TECHNOLOGY
IN STONECUTTERS ISLAND SEWAGE TREATMENT
WORKS
(Final Report)
Research and Development Section
Electrical & Mechanical Projects Division
Drainage Services Department
EXECUTIVE SUMMARY
The objectives of this R&D Item No. RD2047 - Application of Hydroelectric Technology in Stonecutters Island Sewage Treatment Works (SCISTW) are to investigate the technical feasibility of constructing a pilot hydropower plant in one of the Vertical Outlet Wells in SCISTW and to estimate its cost effectiveness if installed. PolyU Technology & Consultancy Company Ltd. was commissioned in February 2007 to undertake an assignment under the Consultancy Agreement No. DEMP/06/19 for this R&D Item.
Literature studies and market searches were conducted and relevant information of similar project was collected. It is recommended that a hydropower plant with a three-phase asynchronous generator and a basic propeller type turbine can be installed in the Vertical Outlet Well of SCISTW. By utilizing the net available pressure of the outflow effluent, the hydropower plant can generate electricity to supply some of the E&M equipment in SCISTW.
Site measurements, including effluent outflow velocities, were made for estimation of the static and dynamic heads of the outflow effluent inside the Vertical Outlet Well. A hydropower plant of 45kW capacity is proposed to be installed in the Vertical Outlet Well of Sedimentation Tanks Nos. 40 & 42. The designed effluent flow rates of the hydropower plant are in the range of 1.1 to 1.25 m3/s while the designed available net head is from 4.5 to 5.5m. Possible options in installing the hydropower plant at the Vertical Outlet Well were investigated. Taking into account of technical aspects and site constraints, the configuration with the generator and turbine integrated into one unit and mounted inside the Vertical Outlet Well is recommended. A motorized control valve will be installed on top of the Vertical Outlet Well to control the effluent flow to the hydropower plant. The generated electricity will supply to an existing electrical switchboard in SCISTW, in parallel with the electricity supply of CLP, i.e. the hydropower plant to be grid-connected.
The rated generation power of the proposed hydropower plant will only be about 45kW and is within the 200kW limit under the “Technical Guidelines on Grid Connection of Small-scale Renewable Energy Power Systems” issued by
hydropower plant is still required to be submitted to him for formal approval and whether standby charge will be required for the proposed grid-connected hydropower plant can be evaluated after this hydropower plant project has been formally approved for implementation.
It is expected that the proposed hydropower plant can provide a yield of about 263,000 kWh per year. The saving in electricity cost is estimated to be HK$201,185 per year based on that no standby charge will be required by CLP. The environmental benefit is 62.4 Metric Ton Carbon Equivalent per year or 229 Metric Ton CO2 Equivalent per year. The estimated capital cost of installing
the hydropower plant is about HK$5M. It gives a payback period of 26 years if only the financial aspect is to be considered.
Although the financial benefit of this project may not be very attractive, it is considered worthwhile further exploring the application of hydroelectric technology at SCISTW in view of its environmental benefit in the reduction of greenhouse gas emission. If the pilot hydropower plant is decided to be installed, it will be able to be put into operation in end 2009. By then, more knowledge and experience in operating the hydropower plant could be obtained. It is also noted that the HATS Stage 2A project is undergoing, in which additional Sedimentation Tanks and their Vertical Outlet Wells will be built. If civil requirements of hydropower plant(s) are incorporated at the early stage of this project, the hydropower plant(s) can be designed with a lesser capital cost and better maintainability. Further study on the hydropower plants for the HATS Stage 2A project is recommended.
Consultancy Agreement No. DEMP/06/19
Application of Hydroelectric Technology
in SCISTW
( Final Report )
January 2008
Submitted by
T
ABLE OFC
ONTENTSPage No.
1 INTRODUCTION ... 4
1.1 Background...4
1.2 Scope of the Assignment ...4
1.3 Structure of the Report...5
2 LITERATURE STUDIES ON HYDROELECTRIC TECHNOLOGY ... 7
3 SUITABLE TYPES OF TURBINES AND GENERATORS... 10
3.1 Suitable Types of Turbines... 10
3.2 Suitable types of generators... 13
4 INFORMATION OF SIMILAR PROJECTS ... 15
4.1 A 200 kW hydro plant in Puan Hydro, Korea... 15
4.2 A micro hydro scheme at a waste water treatment plant in Emmerich of Germany... 16
4.3 A small hydroelectric station for the new waste water treatment plant in Amann of Jodan ... 17
4.4 A 1.35 MW hydro plant at The Point Loma Wastewater Treatment Plant ... 18
5 TECHNICAL DETAILS AND BUDGETS OF SUITABLE TURBINES AND GENERATORS ... 19
5.1 Tyco-Tamar Design in Australia... 19
5.2 Gugler Hydro Energy GmbH from Austria ... 23
5.3 Kubota Corporation of Japan ... 27
6 MEASUREMENT OF FLOW VELOCITY OF THE FINAL EFFLUENT IN THE VERTICAL WATER OUTFLOW WELL ... 29
6.1 Equipment specification... 29
6.2 Results of measurements and estimations ... 30
7 ESTIMATION OF STATIC AND DYNAMIC HEADS OF THE FINAL EFFLUENT IN THE VERTICAL WATER OUTLET WELL... 32
8 DESIGN REFERENCES... 33
8.1 Design Inputs ... 33
8.2 Relevant Standards, Code of Practice and other Manuals/References... 33
9 PROPOSED HYDROELECTRIC TECHNOLOGY APPLICATION IN SCISTW... 36
10 POSSIBLE OPTIONS FOR THE PROPOSED HYDROELECTRIC SYSTEM... 38
10.1 General... 38
10.2 Turbine / Generator SET... 38
10.3 Control Valve/Gate... 45
10.4 LV Switchboard ... 47
11 HYDRAULIC DESIGN ... 54
11.1 Surge PRESURE and Back PRESSURE... 54
11.2 Conclusions... 56
12 CIVIL & MATERIAL REQUIREMENTS ... 57
12.1 General... 57
12.2 Support for the Turbine and Genentor... 57
12.3 BoTtom metallic screen and its Support... 58
12.4 The guide tubes and its Support... 59
12.5 Support for the Electricity Cables/conduits... 60
13 ELECTRICAL & MECHANICAL WORKS... 61
13.1 Major Electrical Equipment ... 61
13.2 Hydro-Turbine ... 61
13.3 Generator... 63
13.4 LV Switchboard and control panel... 64
14 CLP’S REQUIREMENTS FOR ON-GRID CONNECTION... 75
15 OPERATION AND CONTROL OF THE HYDROPOWER PLANT ... 83
15.1 Normal Start-up... 83
15.2 Normal Shut-down ... 83
15.3 Emergency Shut-down ... 84
15.4 Failure of Power Supply... 84
15.5 Control and INstrumentation... 85
15.6 Maintenance issues... 85
16 SPECIFICATIONS OF THE PROPOSED HYDROELECTRIC SYSTEM... 86
17 PROJECT INTERFACE AND IMPLEMENTATION SCHEDULE... 88
17.1 Project Interface... 88
17.2 Implementation Schedule ... 88
18 BUDGETING... 89
18.1 Capital Cost and Recurrent Cost ... 89
19 ANNUAL ENERGY YIELD, FINANCIAL AND ENVIRONMENTAL BENEFITS... 91
19.1 Power & Energy Generation... 91
19.2 Power Utilization... 92
19.3 Environmental Benefits ... 92
20 CONCLUSIONS & RECOMMENDATIONS ... 95
20.1 General... 95
20.2 E & M EquipmeNt & Civil Work... 95
20.3 Construction Method Statement... 95
1 Introduction
1.1
BACKGROUND
The Stonecutter Island Sewage Treatment Work (SCISTW) is capable of handling a daily sewage flow of 1.7 million m3/d. After treatment, the effluent is discharged via a 1.7 km
long submarine outfall to the western approach of the Victoria Harbour. There are 36 sedimentation tanks (excluding two prototype tanks) and 18 associated vertical outflow wells in SCISTW.
The vertical drop distance of water inside the vertical outflow well can be as high as 5.5 - 8m. The velocity near the bottom of the well can be greater than 7 m/s. Due to the difference in the static water levels, there is a potential to recover pressure energy of the effluent water at the vertical outflow well of the treatment works to generate electricity by a water turbine generator.
In February 2007, the Drainage Services Department (DSD) commissioned PolyU Technology & Consultancy Company Limited (PTeC) to undertake an assignment under the “Consultancy Agreement No. DEMP/06/19 – Application of Hydroelectric Technology in SCISTW” (hereinafter called “The Assignment”), with the objective to investigate the technical feasibility and cost effectiveness for constructing a pilot hydropower plant for the generation of electrical energy to be used as part of the electricity supply to the SCISTW by utilizing the net available pressure of the outflow.
1.2
SCOPE OF THE ASSIGNMENT
The scope of this Assignment comprises: -
To carry out literature studies and market searches to collect the up-to-date information including the technical data and job references, of the hydroelectric technology, in particular the application of low head micro-hydroelectric technology in sewage treatment plants;
To investigate the possibility of applying the hydroelectric technology in SCISTW from the engineering point of view, including the required civil modification works, liaison with CLP Power for connecting the hydroelectricity generation plant to his electricity supply grid, etc.; and
To carry out a preliminary assessment on the cost-effectiveness of applying the hydroelectric technology in SCISTW
1.3
STRUCTURE OF THE REPORT
Following the introductory section, the remainder of this Report is structured as follows:-
Part A – Literature Studies and Market Searches
Section 2 – Literature Studies on Hydroelectric Technology
This will review the advantages and disadvantages of hydroelectricity, and their relevancy to this project.
Section 3 – Suitable Types of Turbines and Generators
This section will discuss the type of turbine and generator suitable for the application of this project.
Section 4 – Information of Similar Projects
A few examples of applications in water/sewage treatment plants will be given in this section
Section 5 – Technical Details of Suitable Turbines and Generators
This section will present technical details of some suitable turbines and generator collected from suppliers.
Part B –Technical Feasibility of the Proposed Hydroelectric Technology
Section 6 – Measurement of Flow Rate of the Final Effluent in the Vertical Water OutletWell
This section will present the measurement results of the flow rate.
Section 7 – Measurement of Static and Dynamic Heads of the Final Effluent in the Vertical Water Outlet Well
This section will present the measurement of static and dynamic head of the flow in the Vertical Water Outlet Well.
Section 8 – Design References
This section will contain the design references for the pilot hydropower plant. Section 9 – Proposed Hydroelectric Technology Application in SCISTW
This section will highlight the description of the proposed hydro turbine system. Section 10 – Possible Options for the Proposed Hydroelectric System
This section will summarise the options recommended for the pilot hydropower plant. Section 11 – Hydraulic Design
This section will provide the hydraulic design for the pilot hydropower plant. Section 12 – Civil Requirements
Section 13 – Electrical & Mechanical Works
This section will present the electrical and mechanical works for the hydropower system. Section 14 – CLP’s Requirements for On-grid Connection
This section will stipulate the CLP’s requirements for the on-grid connection of the proposed hydroelectric system.
Section 15 – Operational and Control of the Proposed Hydroelectric System
The operational requirements of the hydroelectric system will be discussed in this section. Section 16 – Specifications of the Proposed Hydroelectric System
The construction method statement of the hydroelectric system will be provided in this section.
Section 17 – Project Interface and Implementation Schedule
This section will discuss the project interface and present a tentative implementation programme for the hydroelectric system.
Part C – Cost-Effectiveness of the Proposed Hydroelectric Technology
Section 18 – BudgetingThis section will discuss the estimated costs of the whole project
Section 19 – Annual Energy Yield, Financial and Environmental Benefits
This section will discuss the annual energy yield, financial and environmental benefits of the whole project
Part D – Conclusions and Recommendations
Section 20 –Conclusions and RecommendationsPart A – Literature Studies and Market Searches
2 Literature Studies on Hydroelectric Technology
Within the various sewage treatment plants in DSD, there are various locations of vast water flow rate at low water head. DSD would like to explore the possibility of applying hydroelectric system at these locations to recover partly the energy in the water flow, without scarifying the performance of the sewage treatment plants.
If the concept can be applied, then it will
1. help to boost the applications of renewable energy in Hong Kong; 2. help to reduce the emission of green house gases in Hong Kong; 3. reduce electricity bills of DSD;
4. also act as a response to government initiatives of green features in infrastructure projects.
The following paragraphs are summary of literature studies on hydroelectric technology; a list of reference is attached at the end of this chapter.
Hydro-electricity basically has following positive aspects: 1. Hydroelectric energy is a renewable energy source. 2. No carbon dioxide is emitted as a result of hydropower.
3. Hydroelectric energy is non-polluting. It does not cause chemical pollution of ground or water or the release of heat or noxious gases.
4. Hydroelectric energy has no fuel cost and has relatively low operating and maintenance costs, so it is a good investment in times of inflation and can provide very low cost electricity.
5. Hydroelectric stations have a long life. Many existing stations have been in operation for more than half a century and are still operating efficiently.
6. Hydropower station efficiencies of over 90% can be achieved, making it the most efficient of energy conversion technologies.
7. Hydroelectric energy technology is a proven technology that offers reliable and flexible operation.
9. A dam can be a useful resource for leisure, fishing, irrigation or flood control.
Point #6 may not apply in the sewage treatment plants of DSD. 90% efficiency can only be achieved in hydroelectric station of very large scale and high head.
Point #8 does not apply in the proposal of this case. The output power will not be controlled but be simply fed into the grid.
Obviously Point #9 does not apply in the sewage treatment plants of DSD.
There are however some social, ecological and hydrological effects have to be taken into consideration when planning a hydroelectric power station. These effects can be enormous if the system is very large:
1. Hydropower is only suitable for sites with large volumes of flowing water. Decreased rainfall, due to climate change, would reduce the electricity available.
2. Considerable capital investment is required, especially for large schemes.
3. Dams cause large areas upstream to be flooded. This may cause displacement of people and will destroy animal habitat and flora.
4. Flooded vegetation will rot anaerobically and emit methane, a potent greenhouse gas. 5. The dams and diversion of water may also change the groundwater flows in the local
area and this can change the ecology of the area.
6. Damming the river reduces flooding which reduces the amount of silt carried downstream. It also increases the amount deposited in the dam. This may mean that the dam has to eventually be dredged while downstream there is reduced fertility in the soil.
The flow rates (as detailed later) in the sewage treatment plants of DSD are large and relatively fairly constant (as against rainfall throughout a year). Hence Point #1 is not applicable. No additional dam or reservoir is required to be constructed to hold the water. Hence the Point 3 to 6 are not applicable. Fortunately, most of the demerits mentioned here are not valid in the sewage treatment plants of DSD, maybe with only Point #2 as the exception. However, in the proposed pilot project, only one pilot hydro generator plant will be installed in one of the 18 vertical outflow wells at SCISTW. Hence the capital investment will not be too large. However, there is one specific point which need to be considered seriously in application of hydro plant in sewage treatment works as compared to other areas of applications. That is sewage water to be highly corrosive and hence all the involved equipment have to have enough protection against it. This point will add considerable amount to the capital cost of the equipment and support structure of the equipment.
Therefore, overall speaking, application of hydroelectricity technology to recover energy from sewage water in general has more merits than demerits.
Reference:
Adam Harvey, “Micro-hydro Design Manual”, Intermediate Technology Publications 1993. Jiandong Tong, “Mini Hydropower”, John Wiley & Sons, 1996.
FM Griffin, “Feasibility of Energy Recovery from a Wastewater Treatment Scheme”, Proceedings of Hydropower Developments Conference, IMechE, 1997.
Edward, B.K., “The economics of hydroelectric power”, Cheltenham, UK ; Northampton, MA : Edward Elgar, 2003
3 Suitable Types of Turbines and Generators
Turbine and generator are the two most important components in a hydroelectric project. This
Section will discuss the suitable types of turbines and generators to be used in the pilot
project.
3.1
SUITABLE TYPES OF TURBINES
Turbines can be classified as high head (more than 100 m), medium head (20 to 100 m) or low head (less than 20 m) machines. Turbines are also be classified by their principle of operation and can be either impulseturbines or reaction turbines.
Table 3.1: Selection of turbine types based on available water head
high head medium head low head
Impulse turbines Pelton Turgo cross-flow multi-jet Pelton Turgo cross-flow Reaction
turbines Francis propeller
Kaplan
Turbine selection is based mostly on the available water head, and less so on the available flow rate. In general, impulse turbines are used for high head sites, and reaction turbines are used for low head sites. In most sewage treatment plants of DSD, low head should be the usual cases. Hence, only reaction turbines are discussed here.
The reaction turbines considered here are the Francis turbine and the propeller turbine. A special case of the propeller turbine is the Kaplan. In all these cases, specific speed is high, i.e. reaction turbines rotate faster than impulse turbines given the same head and flow conditions. Therefore a reaction turbine can often be coupled directly to a generator without requiring a speed-changing mechanism. Some manufacturers even make integrated turbine-generator sets of this type. Significant cost savings are made in eliminating the speed changing mechanism and the maintenance of the integrated hydro unit is very much simpler. Actually, the Francis turbine is more suitable for medium heads than low heads, while the propeller is more suitable for low heads.
Figure 3.1 Selection of turbine based on available water head and power output (Source:
http://www.tamar.com.au/)
Francis turbines can either be volute-cased or open-flume machines. The spiral casing is tapered to distribute water uniformly around the entire perimeter of the runner and the guide vanes feed the water into the runner at the correct angle. The runner blades are profiled in a complex manner and direct the water so that it exits axially from the centre of the runner. In doing so, the water imparts most of its pressure energy to the runner before leaving the turbine via a draft tube.
The Francis turbine is generally fitted with adjustable guide vanes. These regulate the water flow as it enters the runner and are usually linked to a governing system which matches flow to turbine loading in the same way as a spear valve or deflector plate in a Pelton turbine. When the flow is reduced the efficiency of the turbine falls away.
The basic propeller turbine consists of a propeller, similar to a ship's propeller, fitted inside a continuation of the penstock tube. The propeller usually has three to six blades, three in the case of very low head (just a few meters) units and the water flow is regulated by static blades or gates just upstream of the propeller. This kind of propeller turbine is known as a fixed blade axial flow turbine because the pitch angle of the rotor blades cannot be changed. The part-flow efficiency of fixed-blade propeller turbines tends to be very poor.
Figure 3.3: Axial flow propeller turbine
For the intended location on the application in SCISTW, the head is low (less than 10 m) and there are more physical constraints in installing Francis turbine, an axial flow propeller turbine is more suitable for installation, such that the propeller is installed with its axis is vertical.
Kaplan turbines, is a special type of propeller trubine, in which the pitch of the blades and the guide vanes can be adjusted. They are well-adapted to wide ranges of flow or head conditions, since their peak efficiency can be achieved over a wide range of flow conditions by controlling the gates openings and the pitch angles of the blades. Semi Kaplan turbines are the same as Kaplan turbines, but now the guide vanes are fixed, only the pitch of blades can be changed.
Figure 3.5 A drawing showing arrangement for a vertical axis “Saxo” axial flow Kaplan turbine (Source – Bofors-Nohab brochure “Small scale hydro turbine program” 5702) Anyway, the flow rate at the intended location is relatively constant, hence basic propeller type turbine, not Kaplan type, is more preferable to increase the robustness of the trubine (need no blade angle changing mechanism) and to reduce the complication in control. However, Kaplan type turbine can also be considered.
3.2
SUITABLE TYPES OF GENERATORS
For the power range of tens of kilowatt grid-connected renewable energy systems, the commonly used generators are:
o Three-phase synchronous generator and
o Three-phase asynchronous generator (also commonly referred as three-phase induction generator).
In theory, any DC generators can also be used and then DC can be converted to three-phase AC via a three-phase grid-connected inverter. However this configuration is not recommended for the proposed system, due to the overall efficiency is low for this configuration in the proposed power range and the complications in the maintenance of the
Induction generators are generally more appropriate for relatively smaller systems (in tens/hundreds kilowatt, not megawatt scale). They have the advantage of being rugged, almost maintenance-free and cheaper than synchronous generators (around 10% to 25% lower in price for the range of tens of kilowatt). In fact, the choice on synchronous generators is quite limited for power range of tens of kilowatt. The induction generator is, in fact, a standard three-phase induction motor, wired to operate as a generator. Hence the choice of induction generators at tens of kilowatt power range is many. Induction generators can also allow for a wider variation of shaft speed (hence the water flow rate).
Synchronous generators are generally appropriate for multi megawatt systems. They have the advantage of slightly higher efficiency and the excitation is directly controllable. Hence the excitation can be controlled for maintaining the stability, VAR compensation and voltage regulation of the power grid.
In the proposed hydro plant, it is recommended to use induction generator. The reasons are:
o The water flow rate in the proposed hydro plant is likely to have some variations (although small) due to the variation of amount of the incoming sewage water. Induction generator is more capable in coping with these variations.
o In the proposed system, the expected range of power is tens kilowatt. It has little impact of the stability of the very large power grid of CLP Power. It is not required to control the excitation of the generator of this hydro plant to help to stabilize the power grid.
o The efficiency of induction generator at tens/hundreds kilowatt range is well over 90% and it is only slightly (1 to 2 %) less than that of synchronous generator.
o The capital cost of induction generator of this power range should be 10% to 25% lower than that of synchronous generator.
o The only regular maintenance required for induction generations of this power range is the regular lubrication of the shaft bearings and the replacement of shaft bearing after long years of services. While these maintenance items are also required by synchronous generators, synchronous generators need regular replacements of carbon brushes and polishing of slip rings. Hence the maintenance cost of an induction generator of this power range should be only 40% to 70% that of a synchronous generator.
o The advantage of using synchronous generator as VAR compensator is not an important point in this case.
4 Information of Similar Projects
This Section gives a few examples of applications of hydroelectricity in water/sewage
treatment plant in the world. One of it is as small as only 13 kW, while there is also an
example of 1.35 MW rated output from the generator. This illustrated that the applications are
in general feasible.
4.1
A 200 KW HYDRO PLANT IN PUAN HYDRO, KOREA
The turbine generator unit is located in an underground powerhouse which delivers water to a water treatment plant, as well as providing electrical power to the facility.
Turbine: 500mm Propeller type
Generator: rated power 200 KW @ 1200 RPM Rated head: 19.6 m
Rated flow: 1.18 m3/sec
The 500 mm Propeller turbine
Water treatment facility Dam feeding the facility 500 mm runner Figure 4.1: Photos of the hydro plant in Puan Hydro, Korea (Source :
4.2
A MICRO HYDRO SCHEME AT A WASTE WATER
TREATMENT PLANT IN EMMERICH OF GERMANY
This is a very small hydro plant at a waste water treatment installation.
Technical Data:
o
Average output power: 13 kW
o
Water head: H=3.6 to 3.8 m
o
Water flow rate: Q = 400 l/s
o
Generator type: Asynchrongenerator 15 kW, 400V/50Hz
o
Expected annual yield: 65,000 kWh
Figure 4.2: Photos of the hydro plant at Emmerich of Germany (Source: http://www.people.freenet.de/hydropress/index_Hp_neu_Flyer.htm)
4.3
A SMALL HYDROELECTRIC STATION FOR THE NEW
WASTE WATER TREATMENT PLANT IN AMANN OF
JODAN
The town of Amann of Jodan has decided to equip itself with a new wastewater treatment plant. In this region, the purification of water is of vital interest and the volume of water to be treated is high: 277,000 m3/day. The engineers who designed the installation, which was
commissioned in 2005, found a way to reduce the operating costs of this type of installation. Yearly production has been targeted at 21,900,000 kWh in the long run by turbining of waste water upstream and downstream from the station. The company that is going to build and operate the new sewage treatment plant in Jordan, entrusted the turbining design to a minihydraulics laboratory in Switzerland. This laboratory decided to use the height difference between the town of Amann (site of the pre-treatment plant) and the sewage treatment plant in As Samra (103.5 m), in order to produce electricity between the outlet of the treatment plant and the run-off into the Oued Duleil (47.8 m).
The company also claimed that there is great potential for electricity production in a treatment plant, and most sites do not use this potential. Indeed, the digestion gas (biogas) that is produced can be transformed into electricity thanks to a TOTEM (Total Energy Module) and surplus hydraulic pressure can be turbined. When the conditions to use these two potentials are combined, a sewage treatment plant can produce more electricity than it consumes. The engineers of the company realized that the height difference and flow were financially interesting at the Amann site. They decided to recover the surplus pressure at the entrance to or at the outlet of the sewage treatment plant by replacing the dissipating valves with turbo generators thus allowing for the production of electricity. They distinguish between two types of energy recovery. In the first type, raw sewage is turbined at the outlet of the sewage pipes that transport the waste water from the town upstream from the treatment plant. In the second type, treated water from the treatment plant is turbined at the outlet of a pipe or at a stream or river, like in a conventional hydro-electric installation.
The town of Amann will make significant energy savings using the principle which was decided upon. Indeed, sewage treatment plants use a great amount of energy. The driving force needed for the sifters, mixers, pumps, fans, etc. consume great quantities of electricity.
4.4
A 1.35 MW HYDRO PLANT AT THE POINT LOMA
WASTEWATER TREATMENT PLANT
The Point Loma Wastewater Treatment Plant of San Diego (California, USA) is located on a
bluff above the Pacific Ocean. Treated wastewater (“effluent”) is discharged into the ocean
through a 7.2 km ocean outfall after a 27-m drop from the plant to the outfall. A 1,350
kilowatt hydroelectric plant captures the energy of the effluent as it flows down the outfall
connection. The power plant, partially funded by a grant from the California Energy
Commission, produces up to 1.35 megawatts
for sale to the electric grid, enough power to
supply energy to 10,000 homes.
Opened in 1963, the Point Loma Wastewater Treatment Plant treats approximately 662,000 m3/day of wastewater generated in a 1,165-km2 area by more than 2.2 million residents in 12
municipalities. Located on a 16-ha site on the Point Loma bluffs in San Diego, the advanced primary treatment plant has a capacity of 908,400 m3/day.
Figure 4.3: The 1.35 MW generator of the hydroelectric project being installed in the
Point
Loma Wastewater Treatment Plant (source: Wastewater Department, City of San Diego
5 Technical Details and Budgets of Suitable Turbines and
Generators
The following turbine and generator suppliers have been approached and those gave responses are:-
(i) Tyco-Tamar Design of Australia (ii) Gugler Hydro Energy GmbH of Austria
(iii) Kubota Corporation of Japan
Data were collected from these of turbine and generator suppliers. This section will present those in the relevant rating range to the proposed project.
5.1
TYCO-TAMAR DESIGN IN AUSTRALIA
Tyco-Tamar Design in Tasmania of Australia can supply series of micro to small trubine/generator set with power output from the generator varies from less than a kw to hundreds of watt. Those suitable ones (both in available water head and the rated power, hence the estimated flow rate) off the shelf are high-lighted in red in the table.
Table 5.1: Models of micro to mini turbine generator sets from Tyco-Tarmar Design Co. Ltd.
Turbine
Type Code Head range (m) Range (kW).Electrical Pelton LCP1 16 to 100 0.1 to 3
Turgo Impulse LCT1 6 to 42 0.1 to 3
Pelton AP2 28 to 120 0.85 to 9.1
" " AP3 34 to 150 1.9 to 15
Turgo Impulse AT1 20 to 70 0.8 to 7
" " AT2 10 to 90 0.49 to 15 " " AT3 6 to 80 0.45 to 15 " " AT3 twin 4 to 50 0.25 to 15 Pelton SP3 60 to 150 6 to 24 " " SP3 twin 60 to 150 8 to 38 Turgo Impulse ST3 55 to 100 12 to 34 " " ST3 twin 45 to 70 19 to 34 " " ST4 25 to 120 7 to 77 " " ST4 twin 25 to 80 16 to 90 Pelton SP4 80 to 160 19 to 60 " " SP4 twin 80 to 110 38 to 63
Turgo Impulse ST6 30 to 200 22 to 440
" " ST6 twin 30 to 190 50 to 640
Pelton SP6 190 to 260 200 to 330
Turbine
Type Code Head range (m) Range (kW).Electrical Francis F6 2 to 20 0.1 to 8.5 " " F9 2 to 30 0.5 to 45 " " F10 2 to 50 0.8 to 70 " " F12 2 to 50 0.9 to 104 " " F14 2 to 50 1.4 to 153 " " F16 2 to 50 2.0 to 220 " " F18 2 to 50 2.8 to 300 Turbine
Type Code Head Range (m) Range (kW)Electrical Semi Kaplan FS2 - 110 1 to 20 0.3 to 3.5 " " FS2 - 135 1 to 20 1.7 to 15.4 " " FS2 - 165 1 to 20 2.6 to 23 " " FS2 - 200 1 to 20 3.7 to 33 " " FS2 - 245 1 to 20 5.7 to 50 " " FS2 - 300 1 to 20 8.5 to 75 " " FS2 - 365 1 to 20 12.6 to 113 " " FS2 - 450 1 to 20 19.2 to 171
Figure5.1: An example of a 110 kW Semi-Kaplan turbine, Model FS2-365, (with hydraulically operated turbine blades) at assembly stage (Source: Tyco-Tarmar Design Co. Ltd.)
Figure 5.2: Left: Hydralical power pack with PLC for the controlling the main inlet valve and the blades of the semi-Kaplan trubine to maintain optimum efficiency. Right: The main electrical cabinet which contains the electrical switch gear, gnerator protection, local power
distribution circuit breakers, a PLC, and other asscoiated control and electrical equipment. (Source: Tyco-Tarmar Design Co. Ltd.)
As mentioned in previous section, Francis type trubine is not recommended due to the head and the physical constainted in the site, only Kaplan or semi-Kaplan trubine from this company will be considered. Then, it seems that the most appropirate one is model FS2-245 semi-Kaplan turbine/generator set: the head can range from 1 to 20m, while the output power ranges from 5. 7 to 50 kW. The company claims that units can be designed and manufactured to suit the particular site to gain maximum efficiency.
5.2
GUGLER HYDRO ENERGY GMBH FROM AUSTRIA
Gugler Hydro Energy GmbH is a company of 80-year old and she specializes in small trubine. She claimes that she is worldwide successful as complete provider of small hydropower plants with its innovative products.
Gugler Hydro Energy GmbH offers a three-blade Kaplan turbine (model: Gugler KT 50) of turbine diameter of 0.5m, it has mannual adjustable runner blades, fixed wicket gates, the other technical details are:
Net head range (Hn): 1-6 m
Discharges rate range (QA): 300-1,500 litre/sec Rated trubine output (PT): 2.5 – 60 kW
Rated generator output (PG): 1.8 to 50 kW Turbine speeds (n1): 350-1,000 rpm Runaway speeds (nd): 1,200-3,200 rpm
Generator speed (n2 at 50 Hz/60 Hz): 1500-1800 rpm
Operation curves of the KT-50 turbine/generator set is shown in the following figure.
Figure 5.3: Operation curves of the KT-50 turbine/generator set of Gugler Hydro Energy GmbH
Another suitable candidate for the proposed project from Gugler Hydro Energy GmbH is its KT-35 model. Its technical details are:
A three blade Kaplan runner Runner diameter 355 mm
Manual adjustable runner blades Fixed wicket gates;
Net head range (Hn): 1-6 m
Discharges rate range (QA): 100-750 litre/sec Rated trubine output (PT): 2.5 – 40 kW Rated generator output (PG): 1.8 to 35 kW Turbine speeds (n1): 350-1,000 rpm Runaway speeds (nd): 1,200-3,200 rpm
Generator speed (n2 at 50 Hz/60 Hz): 1500-1800 rpm
Figure 5.5: Operation curves of the KT-35 turbine/generator set of Gugler Hydro Energy GmbH
5.3
KUBOTA CORPORATION OF JAPAN
Kubota Corporation established in 1890 and now is a stock-listed company at Tokyo, Osaka, New York and Frankfurt. It has about 24,000 employees and a net sales amount of US$600 million/year. Kubota can supply a turbine/generator set of 45 kW rated power output suitable for this project.
Figure 5.6: Operation curves of the 45 kW Turbine – gnerator set from Kubota Corporation (Note: the term “reverse running pump turbine” is used here in the manufacturer’s data sheet,
Part B –Technical Feasibility of the Proposed
Hydroelectric Technology
6 Measurement of Flow Velocity of the Final Effluent in
the Vertical Water Outflow Well
The water flow rates at three different points inside one of those deep vertical outflow wells were measured through tailor-made supporting rigs and a test instrument procured specifically for this project. The measurement was conducted on 23rd July 2007, from 9:00 am
to 5:30 pm.
6.1
EQUIPMENT SPECIFICATION
Test device - Safety factor = 1.25 - Anticorrosive materials Flow meter- Range of measurable flow velocity ~ 0 to 9.8 ms-1
- Real-time monitoring - Anticorrosive materials
6.2
RESULTS OF MEASUREMENTS AND ESTIMATIONS
Measurement Position 1 Depth = 4480 (mm) Effective Depth = 1800 (mm) Time interval = 60 (s) Number of turns - Sample 1 = 879 (Turns), 4.76 ms-1 - Sample 2 = 877 (Turns), 4.75 ms-1 - Sample 3 = 862 (Turns), 4.66 ms-1Average measured flow velocity =
4.72 ms-1
Theoretical maximum flow velocity at that point
5.94 ms-1 Measured/Theoretical= 79% ______________________________________________ Measurement Position 2 Depth = 5980 (mm) Effective Depth 3300 (mm) Time interval = 60 (s) Number of turns - Sample 1 = 1113 (Turns), 6.06 ms-1 - Sample 2 = 1108 (Turns), 6.03 ms-1 - Sample 3 = 1115 (Turns), 6.07 ms-1
Average measured flow
velocity = 6.05 ms
-1
Theoretical maximum flow velocity at that point =
8.05 ms-1
Measured/Theoretical= 75%
______________________________________________
Position 3 (the estimated position of the turbine)
Depth = 7480 (mm)
Effective Depth (the depth is too deep to be measured by the instrument)
4800 (mm)
Theoretical maximum flow velocity at that point =
9.7 ms-1
Estimated flow velocity,
based on Measured/Theoretical=~75 %, as obtained in above 2 measurements 7.2 ms-1 ______________________________________________
Remarks:
1. The conversion from the number of turns to flow rate (in ms-1) is based on the conversion
information provided from the manufacturer of the flow rate sensor.
2. The theoretical maximum flow velocity is calculated from equation of basic free fall in vacuum. Hence there is expected difference between theoretical maximum flow velocity and the actual velocity due to fluid viscosity and air pressure.
3. The reason for measurements cannot be taken for position 3 is the limitation of the length measurement rod, otherwise the mechanical strength of the whole set up will be too weak.
7 Estimation of Static and Dynamic Heads of the Final
Effluent in the Vertical Water Outlet Well
Based on the results of the above section, the velocity of the flow at the position of the turbine is about 7.2 ms-1. Hence the dynamic head at the location = v2/(2g) = 2.64 m
While the static head is estimated to be 4.8 m. Hence the total head in the worst case is 7.44m. Note this is the worse case, as (i) the installation of the guide tube and turbine in the well will reduce the flow velocity, (ii) the velocity of the flow used here is the velocity at the centre of the flow which is the highest, (iii) it may not be a full-bore condition at the top part of the well (the effective head is likely to be 4.5 m).
8 Design references
8.1
DESIGN INPUTS
In this Report, design inputs for the hydropower plant shall include taking references to all statutory requirements, design standards, codes and guidelines, at both local and international dimensions.
8.2
RELEVANT STANDARDS, CODE OF PRACTICE AND
OTHER MANUALS/REFERENCES
The proposed works shall be designed based on the relevant codes and standards that meet the Drainage Services Department, other local government department, and utility companies’ requirements as well as to follow the good engineering practice on similar works. The following codes of practice, standards and other manuals/references with the associated amendments and additions shall be adopted for the design of the Project:
Table 8-1 Relevant Design Standards, Code of Practice and other Manuals/References
For Civil, Structural and Geotechnical Works:
1 General Specification for Civil Engineering Works, Volumes 1, 2 and 3, Civil Engineering Department
2 Stormwater Drainage Manual, DSD
3 Building Department Practice Note for Authorized Persons & Registered Structural Engineers No. 141 — Foundation Design
4 BS 8007 — Code of Practice for Design of Concrete Structure for Retaining Aqueous Liquids 5 BS 8110 — Structural Use of Concrete
6 BS 4482 — Specification for cold reduced steel wire for the reinforcement of concrete 7 BS 4483 — Steel fabric for the reinforcement of concrete
8 BS EN 752-2 — Drains and Sewer Systems Outside Buildings – Performance Requirements 9 BS EN 752-3 — Drains and Sewer Systems Outside Buildings – Planning
10 BS EN 752-4 — Drains and Sewer Systems Outside Buildings – Hydraulic Design and Environmental Considerations
11 BS EN 295 — Vitrified Clay Pipes and Fittings and Pipe Joints for Drains and Sewers 12 BS 5400-1 — Steel, Concrete and Composite Bridges. General Statement
13 BS 5400-2 — Steel, Concrete and Composite Bridges. Specification for Loads
14 BS 5400-4 — Steel, Concrete and Composite Bridges. Code of Practice for Design of Concrete Bridges
15 BS 8010 — Code of Practice for Pipelines
16 BS 4449 — Specification for Carbon Steel Bars for the Reinforcement of Concrete 17 BS 4027 — Specification for Sulfate-Resisting Portland Cement
20 BS 534 — Specification for Steel Pipes, Joints and Specials for Water and Sewage 21 BS 970-1 — Specification for Wrought Steels for Mechanical and Allied Engineering
Purposes. General Inspection and Testing Procedures and Specific Requirements for Carbon, Carbon Manganese, Alloy and Stainless Steels
22 BS 4504-3.3 — Circular Flanges for Pipes, Valves and Fittings (PN designated). Specification for Copper Alloy and Composite flanges
23 CIRIA report No. 78
Mechanical and Electrical Works:
24 Standard Specifications of the Water Supplies Department
25 General Requirements for Electronic Contracts, Specification No. ESG01, Electronics Division, Electrical & Mechanical Services Department, EMSD
26 Supply rules and other requirements of the CLP Power Hong Kong Limited. 27 Renewable Energy Systems and CLP’s Electricity Grid, CLPP
28 Code of Practice for the Electricity (Wirings) Regulations, EMSD
29 General Specification for Electrical Installation in Government Buildings of the HKSAR, Architectural Services Department, ASD
30 Regulations for Electrical Installations, Institution of Electrical Engineers, UK
31 Technical Guidelines on Grid Connection of Small-scale Renewable Energy Power Systems, 2005, EMSD
32 IEEE Standard 1547 for Interconnecting Distributed Resources with Electric Power Systems 33 UL 1741, Inverters, Converters, Controllers and Interconnection System Equipment for Use
with Distributed Energy Resources
34 EA G59/1, Recommendations for the Connection of Embedded Generating Plant to the Public Electricity Suppliers’ Distribution Systems
35 Code of Practice for Energy Efficiency of Electrical Installation, EMSD 36 Guidelines on Energy Efficiency of Electrical Installation, EMSD
37 Addenda to Guidelines on Energy Efficiency of Electrical Installations, EMSD
For Design of Building Services: Electrical Installation
38 Electrical Ordinance 39 IEE/IET Regulation
40 Codes of Practice for Electricity (Wiring) Regulation, EMSD
41 General Specification for Electrical Installation in Government buildings 42 BS 6651 — Code of Practice for Protection of Structures Against lighting
43 CIBSE Code
44 Code of Practice for Energy Efficiency of Lighting Installation, EMSD 45 Guidelines on Energy Efficiency of Lighting Installations, EMSD
46 Addendum No. 1 to Guidelines on Energy Efficiency of Lighting Installations, EMSD
Fire Services Installation
47 Codes of Practice for Minimum Fire Service Installations and Equipment, Fire Services Department (FSD)
49 L.P.C. Rules
50 Requirement of Water Authority
51 BS 5839 — Automatic Fire Detection and Alarm System 52 Fire Offices’ Committee Rules
53 General Specification for Fire Service Installation in Government Buildings, Hong Kong
MVAC Installation
54 The requirement of the Hong Kong Fire Services Department including “Codes of Practice for Minimum Fire Service Installations and Equipment, and Inspection and Testing of Installations and Equipment” issued by the FSD, together with FSD
circulars/letters/amendments.
55 Building Ordinance and the affiliated regulations
56 General Specification for Air-conditioning and Refrigeration, Ventilation and Control Monitoring and Control System Installations in Government Buildings
9 Proposed Hydroelectric Technology Application in
SCISTW
The proposed pilot hydropower plant incorporates a turbine to convert energy in the form of falling effluent water in the vertical outflow well of the sedimentation tanks of SCISTW into rotating shaft power. The static pressure head between the water level of the tank and the water level of the horizontal trench at the bottom ranges from about 4.5 to 6 metres depending on the operating conditions and the exact location of the turbine.
The shaft power is then converted to electricity by a generator coupled to the turbine. The output voltage is expected to be 380 V three-phase AC and then connected to a switchboard and control panel.
The hydro-turbine is designed to work under maximum 6 m static head under operating conditions. The effective static head is about 4.5m while the efficient operating flow rate is from about 1.1 to 1.25 m3/s. The maximum power output from the generator shall be
approximately 45kW to 50kW. Besides, the hydro-turbine shall be designed to cater for the start up under hydro-static /surge conditions that may be as high as 17 metres total head equivalent. This head will be diminished as the turbine flow increases to the normal operating range as specified.
As mentioned above, the estimated maximum power output of the system is about 45kW to 50 kW, and this is basically the maximum allowable output from a turbine with the given possible water head, typical machine efficiency and physical internal dimension constraints of the well. The dimension constraints limited the external size of the whole setup to be within 1.2 m in diameter. Then with reasonable allowance for fixture mounting, the effective diameter of the turbine can only be about 1 m in diameter. After experience gained in this pilot project, this maximum power output for subsequence installation may be increased slightly by increasing the effective diameter of the turbine without affecting the overall external diameter.
Power generated by the hydro-turbine generator will be utilized at the SCISTW to provide co-generated power with the utility to the all electrical installation within SCISTW. All power generated by the hydro-turbine driven generator shall be utilized on site as a reduction in the amount of power received from the utility. There will be no export (to outside of SCISTW) of the power by the turbine generator. The hydro-turbine generator unit shall always operate in conjunction with the utility supply, and shall not operate independently without the utility.
Figure 9.1 Schematic of power flow of the hydro plant
Local LV Distribution
Board
Turbine
Generator
LV
Switchboard
Effluent Outflow Water
10 Possible Options for the Proposed Hydroelectric
System
10.1
GENERAL
Major equipment/facilities to be incorporated in the hydropower plant include turbine, generator, control valve/gate, LV switchboards and control panel. The turbine and the generator will be installed in a vertical outflow well. The control valves/gates will be installed at the top of the well. The LV switchboard and control panel will be installed inside an existing switchboard room near the vertical outflow well. Additional small cable conduits will also be required to be installed between the generator and the LV switchboards/control panel.
10.2
TURBINE / GENERATOR SET
The turbine has to be mounted vertically inside the vertical outflow well in order for the turbine to capture the water flow with minimum civil modification works. Of course, another alternative is to re-route that part of effluent water to a separate structure (next to the vertical outflow well) which houses the turbine in whatever orientation. However, this alternative is not recommended in this report due to the complicated civil modification works involved.
The selected vertical outflow well for this pilot project is #40-#42 (i.e the well between tank #40 and tank #42). The reason of the selection is:
♦ This well is near the upstream end of the effluent water flow (in fact the 2nd first
well along the flow path) under all these wells. In case, there are needs to stop the flow of effluent water under this well during turbine installation period, the operations of other wells are minimally affected.
♦ Although this well is not the first well in the flow (well #44-#46 is the first one), it very often operates together with the well #44-#46. Therefore there will be no effluent water flow from well #44-#46 to well #40-#42.
♦ The reason of not selecting the first well #44-#46 is that there is an existing odour eliminator at the top of the well.
If the odour eliminator can be removed, it is better to install the hydroelectric system to the first well #44-#46.
Figure 10.2: Relative locations of the some of tanks and some of the wells; the pilot project will use Tank #40 and Tank #42, and also Well #40-#42 (not to scale).
Tank #46 Tank #44 Tank #42 Tank #40 Tank #38 Tank #36 Tank #34
A platform, a local LV switchboard is under this here
Well #44-#46
Well #40-#42
Well #36-#38
Figure 10.3: Upper diagram is the cross section of a typical tank and vertical outflow well. Lower diagram is a photo showing the top of one of the vertical outflow wells (covered), note: one can see a very wide access road is at ground level just next to these wells, this road can be
There are three possible ways of mounting the generator
(a) The generator is mounted at the top of the vertical outflow well such that the axle of the generator can be coupled to the axle of the turbine.
Advantages of this method:
♦ The generator is not installed under the water. Hence the construction and requirements is less demanding.
♦ The gravitational loading of turbine and the generator now separately act on two different locations. The weight of the turbine acts on the wall sides of the well, while the weight of the generator acts on the footing mounted on the top of the well. Therefore the civil work to be done on the interior wall of the well is less.
♦ Easy access to the generator for maintenance can be possible. Disadvantage of this method:
♦ The length of the coupling between the generator and the turbine is very long, about 8m. And this coupling shaft/device has to work under the strong effluent water current. There should be at least two intermediate support along the shaft. It is not easy to maintain the mechanical steadiness of the coupling shaft/device even with these supports.
Figure 10.4 shows the location of the proposed turbine / generator set in case (a).
Water Inflow
Turbine Generator
The vertical outflow well
(b) The generator and turbine are integrated into one unit and mounted inside the well Advantages of this method:
♦ This will result a more compact design.
♦ There is no coupling problem between the turbine and the generator. Hence it gives a more stable operation in mechanical terms. The overall efficiency should be slightly higher than case (a).
Disadvantage of this method:
♦ The generator has to work under water and hence the demand on its design is higher.
♦ The whole set has to be hoisted up for maintenance, even if only the generator needs maintenance (it is expected that the generator needs more frequent maintenance than the turbine).
Figure 10.5 shows the location of the proposed turbine / generator set in case (b).
(c) The generator mounted at the same level as the turbine, but outside the well. Advantages of this method:
Turbine
Generator
The vertical outflow well
Water Inflow
Support for the generator/turbine set
♦ The gravitational loading of turbine and the generator now separately act on two different locations. The weight of the turbine acts on the wall sides of the well, while the weight of the generator acts on the footing mounted at ground level outside the well. Therefore the civil work to be done on the interior wall of the well is less.
♦ Easy access to the generator for maintenance. Disadvantage of this method:
♦ The civil work involved will be much larger than case (a) and (b)
♦ There is difficulty in the water sealing for the coupling between the generator and the turbine.
♦ If the axis of the turbine is vertical, then a complicated coupling device is needed between the turbine and the generator. This will reduce the efficiency and reliability of the system. If the axis of the turbine is horizontal, the physical size of the turbine has to be increased, which may not be feasible in this very limited space situation.
♦ This will add certain restriction on the height of the installation of the turbine
Figure 10.6 shows the location of the proposed turbine / generator set in case (c).
After consideration of all the 3 ways of mounting the generator and the site situation, the method of case (b) is recommended in this report. It is a much proven way of mounting. Requirements on the civil aspect, the generator and the turbine will be detailed in later Sections of this report.
Turbine
The vertical outflow well
Water Inflow
Generator
10.3
CONTROL VALVE/GATE
The cross-section of the vertical outflow well is rectangular in shape of about 2m x 1.25 m with effective length of about 5.8 m. After the installation of turbine and its guide tube, there is still room at the side for by-passing “surplus” water flow.
Bottom screen
Figure 10.7: Location of the control gate (side view, not to scale)
Figure 10.8: Location of the control gate (top view, not to scale)
Turbine
Generator
The vertical outflow well Water Inflow
Support for the generator/turbine set Control gate
Vertical guide tube for flow (in doted lines)
Water inflow to turbine
The vertical outflow well (area 2m x 1.25 m)
Control gate
Vertical guide tube for flow (in doted lines) (largest part should be with a diameter of 1 2 m)
Surplus water flow into the side of the vertical guide tube
Turbine & Generator Horizontal guide tube for flow (in doted lines)
Horizontal guide tube for flow (in doted lines)
Effective height of the well = 5.8m
A motorised control valve/gate will be installed on the top of the vertical outflow well for controlling the water flow into the turbine. Hence the gate can be used (i) to start the turbine smoothly at the start of the operation and to remove any large surge pressure on the turbine, (ii) to control the generator to run at about synchronous speed during the grid-connection process, (iii) to control the power output after grid grid-connection is made, and (iv) to ensure the turbine will not run over speed.
10.4
LV SWITCHBOARD
An existing LV switchboard is used to house the LV switchgear that connect the generated electricity from the turbine generator to the existing LV distribution board.
The proposed LV switchboard (2-SWB-003) is inside a switchroom situated near the vertical outflow well (within 60 m of cable length). The location of the switchroom can be shown in
Figure 10.2 or 10.9.
10.5
CABLE & CONDUIT ROUTING
There are power and control cables connecting the LV switchboard and the turbine/generator set. The proposed cable & conduit routing is shown in Figure 10-9.
Figure 10.9 shows the routing of cables/conduits (red lines), from the Well #40-#42, cross Bridge A, along Bridge B, into the room under the platform next to Tank#34 (the red line
Tank #46 Tank #44 Tank #42 Tank #40 Tank #38 Tank #36 Tank #34
A platform, a local LV switchboard is under this here
Well #44-#46
Well #40-#42
Well #36-#38 Bridge B
Figure 10.10 shows part of the routing of cables/conduits (red lines), from the Well #40-#42, cross Bridge A (all under the grid)
Bridge A
Well #40-#42
Figure 10.11 shows part of the routing of cables/conduits (red lines), cross Bridge A, to Bridge B, along Bridge B (all under the grid)
Well #40-#42
Bridge A
Bridge B
Figure 10.12 shows part of the routing of cables/conduits (red lines), along Bridge B ( under the grid), coming out from Bridge B, round a corner and then enter into a room under the
elevated platform next to Tank #34.
Cable in red line
Figure 10.13 shows part of the routing of cables/conduits (red lines): once inside the room under the elevated platform, there are cable trays for running the cables/conduits
Cable in red line above the tray
A hole on the wall for cables to go outside, the other side of
this hole is also shown in last figure
Figure 10.14 shows part of the routing of cables/conduits (red lines): the cable trays run across the ceiling of the room and then move down to enter the bottom of the local LV switchboard
Figure 10.15: A photo shows how cables on the vertical trays entering the raised floor of the local LV switchboard room
11 Hydraulic Design
This section will provide the hydraulic design for the pilot hydropower plant
11.1
SURGE PRESURE AND BACK PRESSURE
11.1.1
Surge Analysis
The purpose of the surge modeling is to assess the surge potential resulting from a shutdown or starting of the operation of hydro-turbine driven hydropower generator during adverse operating conditions. Hydraulic transients or surges (also sometimes called water hammer) are pressure changes that occur any time the velocity of flow changes. Velocity changes in the well by starting or stopping of the flow, sudden closure or opening of a valve or check valve, or the loss of power to pump motors. The most severe surge condition for the purposed turbine location would occur as the start of the flow in the well and results in a sudden change on the mechanical load of the hydro-turbine.
The mathematical relationship between the pressure change, dp, and the change in velocity, dv, is as follows:
dp = a(dv)/g
where: a = water pressure wave speed = about 914 m/s, and g = gravitational constant = 9.8m/sec2
The velocity of flow through the well varies along with the depth of well, but at estimated location of the turbine, the velocity is about 7.2 m/s (from a previous section). Therefore it can be seen that for an abrupt (instantaneous) start of flow condition, the resulting pressure increase would be 914 x 7.2/9.8 = 292.5 m = 672 psi. This is a very large value. In practice, velocity changes must occur over some extended period of time so the resulting pressure spike will be considerably less.
However, now control gate will be installed at the top of the well and will be controlled to open very slowly, the duration of the opening process is in the order of a minute or minutes (say at least 30 second) instead of sub-second range. Hence the surge pressure should not be a problem here, should be at least less than one-thirtieth of the above calculated value, i.e. less than 10m surge pressure. Together with the worse case static head and dynamic head about 7 m (as discussed in a previous section), the total maximum possible transient head should be less than 17m.
17 m transient head is not a high value, and the turbine should be able to handle this transient surge without damage.
11.1.2
“Back Pressure” Issue
The effective cross section area for the flow through the turbine is much less than the cross section of the original vertical outflow well. There may be worries for building up of “back
pressure” and finally sewage water accumulates in the tanks and raise the water level beyond the limit. However, it should be note that there is a by-pass path next to the turbine (please refer to Figure 10.8). Even under the case of a completely closed gate, the sewage water can flow freely down the by-pass path. The cross section of this by-pass path should be at least 0.8m x 1.0m. Even assume the effective length of the vertical well to 5.5m, while assume effective head of 4.5m, the maximum possible flow rate under very restricted flow assumptions (refer to next paragraph) should be well above 2 m3/s, which is much higher
than the maximum expected flow rate of the well. Hence there is so “back pressure” issue in this case; i.e. installation of the turbine should not affect the handling capacity of the tanks. Pressure loss in a pipe: ∆p = λLρω2/(2D)
Where: ∆p is the pressure loss
λ is the coefficient of friction of the pipe L is the effective length of the pipe ρ is the density of the fluid of the flow ωis the vecocity of the flow
D is the effective diameter of the pipe Available pressure in a vertical pipe: ∆p = ρg∆H Where: ∆p is the available pressure
ρ is the density of the fluid of the flow g is the gravity constant (9.81 ms-2)
∆H is the effective length of the pipe
Equating the above two equations to make that the available pressure from the gravity all losses in the flow, this gives
∆H g =λLω2/(2D)
Rearranging it gives:
ω =√(2gD∆H/(λL))
In the proposed case, make a very worst case assumption for the by-pass path: D=0.8 m, ∆H =4.5m, L = 5.5 m, and assume a very rough inner tube surface of λ=0.15, this gives ω = 9.3 ms-1.
Assume the average velocity is only half of the 9.3 ms-1, with a D=0.8 m, the flow rate will be
2.32 m3s-1.
the flow rate through the by-pass path should be less than 3.5 m3s1 when the control valve is
fully opened.
However one should note that with the installation of the control valve and the horizontal guide tube, the water level at the horizontal channel would be raised by 0.3 m. to 0.5 m. Anyway, this still should not affect the top water level of the sedimentation tank, as the horizontal channel is at a level lower than the top water level of the sedimentation tank.
11.2
CONCLUSIONS
(1) The hydraulic analysis shows that the total maximum possible transient head should be less than 17m of water head acting on the turbine.
(2) The “back pressure” should not be an issue in the design due to the existence of a large by-pass path next to the turbine.
12 CIVIL & MATERIAL REQUIREMENTS
12.1
GENERAL
The proposed site for the pilot hydropower plant is discussed in a section above, and the details of the general arrangement of the proposed hydropower plant as well as the associated civil and structural requirements will be discussed in this section.
12.2
SUPPORT FOR THE TURBINE AND GENENTOR
The integrated turbine and generator set will be located in the well at very lower end side. The cross section of the well is rectangular in shape, while the turbine generator is basically circular in shape. The set will be hanged from a support which is mounted at the top of the well, as shown in Figure 10.7.
The dead weight of the turbine and generator set is about 5,000 kg. The maximum transient pressure head is estimated to be 17m with the maximum possible cross section area of the turbine (0.5m)2×π = 0.79 m2. Therefore the total maximum transient loading on the support
is 5000 + 17x0.79x1000=18,430 kg, while the maximum steady loading on the support should be less than 5000 + 7x0.79x1000=10,430 kg. These are the required loading withstand capability for the support of the turbine generator set. The support is expected to be made of galvanised steel of heavy gauge with good corrosive resistant coating (meeting ASTM A 653 standard or equivalent), to allow its long life operation over the sewage water.
[ASTM A 653: Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process]
Additional loadings that may need to be considered for the structure of the metallic support of the turbine generator set are:
additional imposed loads during installation /maintenance/operation process of the plant, including imposed loads due to construction plant,
wind load during installation/maintenance/operation (if appropriate). (That is, this metallic support will also be used to hoist up or low down the turbine generator set in the well
The expected weight of the support should be less than 400 kg. Therefore one has to check whether the existing civil structure around the well can withstand maximum static loading of 10,430 kg + 400 kg = 10,430 kg, and total transient loading of 18,430 kg + 400 kg = 18840 kg. One also has to check the per unit area floor loading capability of the existing civil structure around the well, so that a proper design on the foot padding of the metallic support for the turbine and generator set can be carried out.
Again additional loadings that may need to be considered for the civil structure of the area around the well are:
wind load during installation/operation (if appropriate).
Site investigation reveals that there are wide internal access roads right next to the well, and the area around the well is free (please refer to Figure 10.3). Hence there should not be any problem in using a heavy truck with a large hoisting machine for the civil work, as well as the installation of the guide tubes, the turbine generator set and other equipment.
A preliminary assessment indicates that the existing civil structure should be able to support loading that mentioned above, as the weight of water that each tank can hold is more than 2,800,000 kg. Hence the static load of 10430 kg and transient load of 18840 kg are only a tiny part of the water loading.
12.3
BOTTOM METALLIC SCREEN AND ITS SUPPORT
As a means of providing a safety net for workers during installation and maintenance, as well as a security net to catch any large broken pieces of equipment - say, turbine blade (just imagining very worse cases), a strong rigid metallic screen should be installed at the very bottom of the vertical outflow well before installation of any other things inside the well. The screen should be in metallic grid form of 100mm x 100 mm grid size, made of grade 316 steel bars by welding. The screen should completely cover the whole lower opening (2m x 1.25m) of the vertical outflow well. As the size of the grid is large, its impact on the flow is very minimal.
The screen should be mounted securely by strong anchors onto the fou