Outline of the technology
1.Background and object
Coal is expected to increase the demand owing to the abundant reserves, the expectation of stable supply, and the low price, though the influence of CO2 and other substances on the environment is relatively large compared with other fossil fuels. In the situation, to decrease the emissions of CO2 from coal fired power plants which account for large percentage in the coal utilization field, it is important to develop a power generation technology of higher thermal efficiency than ever, and to bring the technology widespread use over the world.
If coal is utilized as a gas turbine fuel, the adoption of combined cycle power generation system (combination of gas turbine and
steam turbine) realizes higher efficient power generation than that of existing pulverized coal fired power generation. To this point, if coal can remove impurities such as ash and alkali metals, the resulting clean coal can be used as fuel to directly combust in gas turbine.
Regarding the issue, NEDO conducts development of technology of combined power generation system, where the coal is treated by solvent extraction and ion exchange to remove ash and alkali metals to obtain clean coal (Hyper-Coal), which is then directly combusted in gas turbines.
2.What is Hyper-Coal?
A solvent having strong affinity with coal is applied to the coal extraction, and then unnecessary ash is sedimented to remove from the coal to obtain very low ash coal (Hyper-Coal).
3.Hyper-Coal production facilities
(1)Preheating-extraction unit
Coal is extracted by a solvent, and then is treated by rapid filtration to remove residue, thus Hyper-Coal is produced. (Design temperature: 500O
C, design pressure: 3MPa)
The unit produces various grades of Hyper-Coal samples.
(2)Sedimentation-separation unit
The unit is a sedimentation tank having coal extraction performance, (design temperature: 500OC, design pressure: 5 MPa). Vertically arranged five valves collect samples to determine the sedimenting condition of non- dissolved ingredients under pressurized and heated conditions.
Charcoal
Solvent Coal
Solvent penetrates into coal Cohesion of coal becomes weak, and soluble portions of coal dissolve. Insoluble portions and ash are sedimented to remove. Extract residue charcoal
Hyper-Coal
In charge of research and development: Center for Coal Utilization, Japan; National Institute of Advanced
Industrial Science and Technology; and Kobe Steel, Ltd.
Project type: Development and Survey of Next Generation Technology for Coal Utilization, promoted by New Energy
and Industrial Technology Development Organization (NEDO)
Period: 2002-2007 (6 years)
Fig. 1 Conceptual drawing of Hyper coal manufacturing from coal
Coal is charged into the solvent, and the system is pressurized and heated to let the coal portions disperse into the solvent. Insoluble ash is treated by the settler to sediment by gravity to remove as the residue coal. The solvent containing dispersed coal portions is sent to the ion exchange vessels.
Ion exchange vessels remove alkali metals which cause high temperature corrosion.
The material is flash-sprayed into the drying tower to separate the solvent. The solvent is recovered to reuse.
The gas turbine combined cycle power generation system is a power generation system which combines gas turbine with steam turbine. When a gas turbine of 1350oC
level of combustion gas temperature is used, about 20% of CO2 emission reduction is attained compared with the pulverized coal fired power generation system.
Conventional power generation system. Power is generated by combusting the residue coal. Roughly deashed coal
(ash content: 5% or less) Overseas mining site (coal mine)
5.Configuration of Hyper-Coal based high efficiency power generation system
6.Concept of Hyper-Coal based power generation system 7.Schedule of research and development
Post-evaluation
Interim evaluation
Photo 3 Test apparatus for manufacturing Hyper coal continuously
4.Features of Hyper-Coal
- Ash content is decreased to 200 ppm or lower level. Alkali metals (Na, K) are decreased to 0.5 ppm or lower level by ion exchange.
- Calorific value increases by about 10-20% from that of original coal.
- Inorganic sulfur is completely removed.
- Content of solid state trace amount of heavy metals is significantly decreased, (to 1/100 or smaller).
- The residue generated by 30-40% to the original coal during the production stage can be used as general coal.
- The production cost is low, about 950-1,200 yen/ton-HPC. - The HPC has excellent ignitability and burn-off property. - The HPC shows high flowability, and is a good carbon material for direct reduction iron and for smelting nonferrous metals. - Since HPC is rich in volatile matter and is free from ash, it is
excellent gasification raw material, and it is expected to increase high efficiency of gasification.
Fig.2 Fundamentals of Low-Rank Coal Upgrading
3D2. Low-Rank Coal Upgrading Technology (UBC Process)
Outline of technology
1.Background and process outline
Brown and sub-bituminous coal resources accounting for about 50% of coal reserves are called low-rank coal whose applications are limited due to its low heating value and spontaneous combustion property. Many of these low-rank coals, however, are featured such as by low sulfur/ash contents, unlike bituminous coal. So if they could be efficiently upgraded and converted into high-grade high-heating value coal, it will then contribute not only to the security of stable energy supply but
also greatly to environmental problems. The low-rank coal upgrading technology (UBC Process) is under development as a technology to make effective use of such low-rank coal.
This process, an adaptation of slurry dewatering technology of the brown coal liquefaction process, consists of 3 stages; 1) slurry preparation/dewatering, 2) solid-liquid separation/solvent recovery, and 3) briquetting.
Fig.1 Low-Rank Coal Upgrading Process (UBC Process) Scheme
At the stage of slurry preparation/dewatering, after pulvelized high moisture low-rank coal is mixed with recycled oil (normally petroleum light oil), then laced with heavy oil (such as asphalt), and heated in a shell & tube-type evaporator, moisture is recovered as water vapor. This water vapor is sent to the shell side of the evaporator after pressurized by a compressor to use the waste-heat as a heating source, thereby having so far substantially saving energy consumption at the stage of dewatering. Low-rank coal also contains numerous pores and the moisture within them is removed in the course of evaporation. During that time, laced heavy oil is effectively adsorbed onto pore surfaces, thus preventing spontaneous combustion. Moreover, the heavy oil expresses its nature to water repellency, functioning to prevent the re-adsorption of
moisture and accumulation of heat of wetting. The right figure shows this phenomenon conceptually.
Asphalt Slurry dewatering
Slurry preparation Decanter Solid-liquid separation Evaporator (140OC/350kPa) Solvent recovery Recycle solvent
Waste water Upgraded brown coal (UBC)
Raw coal
Upgraded brown coal briquette
Capillary water Surface water
In charge of research and development: Japan Coal Energy Center; the Institute of Applied
Energy; Kobe Steel, Ltd.; Nissho Iwai Corp.
Project type:1. Low-rank coal upgrading technology-related investigation
2. Joint research of technologies applicable to coal producing countries
Period: 1. 1995-1998(4 years) 2. 1999-2004(6 years)
Asphalt
Befor dewatering After dewatering
Selective adsorption of asphalt onto pore surfaces
Photo 1 Briquetted UBC
Photo 2 Low-Rank Coal Upgrading Demonstration Plant
1) Toru Sugita et al: UBC(Upgraded Brown Coal) Process Development, Kobe Steel Engineering Reports, 53, 42 (2003)
Reference
At the stage of solid-liquid separation/solvent recovery, after recycled solvent is recovered from the dewatered slurry by the decanter, the recycled solvent remaining in the pores of upgraded coal is also recovered by the steam tubular drier.
Upgraded coal obtained from UBC Process is still in a powdery state, requiring to be briquetted due to the necessity of transportation except when consumers are located nearby. The upgraded coal, normally binder-less briquettable, can be easily briquetted, using a double roll briquetter. The right figure shows a photo of briquetted upgraded-coal.
2.Development target
1)Upgrading cost
If bituminous coal with a heating value of 6,500kcal/kg is assumed 20 dollars/ton in FOB price, the FOB price of 4,500- kcal/kg sub-bituminous coal is supposed some 13 dollars/ton in calorific equivalent. If it is assumed that, from this, upgraded coal of 6,500kcal/kg should be obtained, the guideline for treatment cost will be set around 7 dollars/ton. Even with advantages of low-rank coal such as its low ash contents and other features borne in mind, it is necessary to target about 7 to 9 dollars/ton for treatment costs.
2)Thermal efficiency for upgrading
Thermal efficiency in the upgrading process needs to be 90% or more so that higher thermal efficiency than at direct low-rank coal firing power plants may be achieved in terms of overall comparison from UBC firing power generation.
3.Development in progress and results
The heating value of upgraded coal, though it is varied depending upon coal properties has been improved to around 6,500kcal/kg, with its spontaneous combustion problem also successfully suppressed. It has also been confirmed that briquetted upgraded-coal is similar to normal bituminous coal in easiness of handling and re-crushing.
Furthermore, upgraded coal, if burnt, quite easily burns itself out to leave almost no un-burnt portion even under low-NOx combustion conditions, assuring that it also has excellent characteristics as fuel.
4.Future assignments and prospective commercialization
A demonstration-plant of 5 tons/day (raw coal-base) built in Cirebon of the Java Barat province, Indonesia, is now in operation, where the Ministry of Energy and Mineral Resources’ Research and Development Agency, Indonesia and the Japan Coal Energy Center are main promoters.
In Asia-Oceania region, there are a lot of low-rank coal resources. The coal mining companies, which have low-rank coal, are highly interested in UBC process, hoping its earlier commercialization.