R ESULT OF SCENARIO ANALYSIS

As the result of scenario analysis 1 and 2, the gap between high demand (19,045 MW) and low demand (17,823 MW) is about 1,200 MW in 2025, whereas the gap between high demand and base demand (18,417MW) is around 600 MW in 2025. The gap is likely to be covered as the amount of the gap is small compared to total peak load. Consequently, it is important to construct the power plant following the power expansion plan [16].

Fig. 5.3 Scenario analysis [MW] [16]

Fig. 5.4 Scenario analysis (Mega Project is delayed) [MW] [16]

According to the scenario analysis 3, the delay of the Mega Project would have a significant influence to peak load. If the Mega Project is delayed for one year, the peak load in 2010 (7,247 MW) will be approximately 1,400 MW lower than base demand (8,621 MW). If the delay is two years, the peak load in 2010 will be about 2,900 MW lower than base demand. However, a delay of the Mega Project does not seem to cause such a big problem as the amount of peak load of general consumption. On the other hand, the power shortage is not caused by a delay of the Mega Project.

Demand analysis indicted a trend that power supply in Libya is expected to increase from 4,420 MW in 2007 to 18,417 MW in 2025 (including the Mega Project – 6,876 MW) and total consumption will reach approximately 70,000 GWh in 2025. Furthermore, it is forecast that the peak load will occurs in summer, especially in August from 2013 as the cooling load is expected to be higher than the heating load. According to the input factor analysis, demand is increased 3.22% due the GDP and 4.64% due the population when 1% of either factor increases. In addition, electricity use rises rapidly when temperatures are higher than 30 degrees or lower than 15 degrees [16].

6 T HE OBJECTIVES OF THE THESIS

Practically only conventional power plants are used in Libya. The main aim of this thesis is the analysis of possible use of the waste heat energy for heating of domestic hot water, space heating, and for driven cooling equipments (absorption chiller) for air conditioning in the summer season.

The solution is divided to the four main parts:

A. SOURCES

a. Conventional power plants (fuels, types, properties, parameters, efficiency) b. Cogeneration power plants (fuels, types, properties, parameters, efficiency) B. NETWORKS

a. Heating distribution networks (central heating – types, properties, parameters, efficiency)

b. Electrical distribution networks (properties, efficiency) C. CONSUMPTION

a. Typical family house (typical consumption of hot water, heat, cold including powers) b. Use of electricity for covering of the necessities of a typical house

Heating Hot water Cooling

Average yearly consumption of electricity c. Using of heat for covering of the necessities of a typical house

Proposal of the concept (approach) Design of the components of the system Average yearly consumption of heat D. EVALUATION

a. Properties of each system

b. Economical evaluation (house, all systems)

7 C ONVENTIONAL T HERMAL P OWER P LANTS

Thermal power plants are one of the main sources of electricity in both industrialized and developing countries, typical realized as a large central power station; more than half of the electricity generated in the world is by using fossil fuels as the primary fuel. Conventional power plants usually convert one third of fuel used to generate power and the rest of the fuel is lost as heat to the atmosphere, often via a cooling tower. Electricity generation in thermal power plants is characterized by the main source of generation being firing fossil fuels such as coal, natural gas or petroleum (oil). Steam is produced in a boiler, and it drives a turbine connected to an alternator. Heat energy is converted to electric energy within the so-called steam cycle.

Fig. 7.1 Coal Fired Thermal Power Plant [60]

A thermal power plant is usually defined by the type of fuel used to heat the water and create steam. Coal, oil, and even solar and nuclear powers can be used to create the steam necessary to run a thermal power plant. Fig. 7.1 shows a coal thermal power plant.

The energy efficiency of a conventional thermal power station, considered as saleable energy as a percent of the heating value of the fuel consumed, is typically 33% to 48%. This efficiency is limited as all heat engines are governed by the laws of thermodynamics. The rest of the energy must leave the plant in the form of heat. This waste heat can go through a condenser and be disposed of with cooling water or in cooling towers. An important class of thermal power station is associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas and in these plants, freshwater production and electricity are equally important co-products.

The Carnot efficiency dictates that higher efficiencies can be attained by increasing the temperature of the steam. Sub-critical fossil fuel power plants can achieve 36–40% efficiency.

Super critical designs have efficiencies in the low to mid 40% range, with new "ultra critical"

designs using pressures of 4400 psi (30.3 MPa) and multiple stage reheating reaching about 48%

efficiency. Above the critical point for water of 705 °F (374 °C) and 3212 psi (22.06 MPa), there is no phase transition from water to steam, but only a gradual decrease in density [17].

The net electric efficiency (η_e) of a generator can be defined by the first law of thermo-dynamics as net electrical output (WE) divided by fuel consumed (QFuel) in terms of kilowatt hours of thermal energy content.

Fuel E

e Q

W

(7.1)

Conventional Power Plant

100Fuels 36-48 Electricity

Heat Losses

Fig. 7.2 Simple scheme for conventional power plants

Total Efficiency

36 . 100 0

36

tot tot = 36%

8 C OGENERATION (CHP)

Cogeneration is simultaneous production of electrical or mechanical energy and useful thermal energy from a single energy source such as oil, coal, natural or liquefied gas, biomass, or solar [18]. In conventional electricity generation, only a small portion of fuel energy is converted into electricity and the remaining is lost as waste heat.

Cogeneration reduces this loss by recovering part of this. Principal applications of co-generation include industrial sites, district heating and buildings [19].

Cogeneration allows the producer to have his own electricity, hot water and steam, if he needs to. In this way, cogeneration reduces the site’s total outside purchased energy requirements and this reduction on energy use compared to independent heat and electricity generation, may, in return, reduce the total cost of utility services, and also the fuel resources. Also the distribution losses, which are an important problem, will be decreased.

Cogeneration is the best means of converting energy source into heat and power coupled with the CO2 reduction potential. Higher fuel consumption efficiencies are gained from producing electricity and, importantly, utilizing the by-product, heat, for use in district heating systems or for individual homes. Other uses include the use of heat or steam for industry such as the paper or steel industry for steam and laundry or hotels for heat.

Cogeneration, simply put, is an opportunity to control and reduce energy costs. Basically, a cogeneration system takes heat that would normally be wasted and uses it to satisfy some or all of the thermal energy requirement. Fig. 8.1 shows simple concept of cogeneration.

Fig. 8.1 Schematic diagram of Cogeneration (CHP) [20]

Although cogeneration has widely been employed for both enhancing the plant profitability and increasing the overall energy efficiency, it is, however, difficult to justify traditional cogeneration in tropical locations since there is little need for the heat produced. Improving system performance and finding new alternative uses or applications of the heat produced from cogeneration are a great challenge. Cogeneration plants usually operate with low capacity during the no heating season or in the summer period as there are no or fewer heating needs.

new applications of the heat produced during this period e.g. using heat as energy carrier for distributed small-scale thermally driven machines. Finding new alternatives for energy applications from waste, like the implementation of thermally driven cooling processes via absorption cooling, is very attractive [18].