GASIFICATION OF COAL TO ENERGY
S. K. ANSARI - CHEMICAL ENGINEER
SEEMA ANSARI - TELECOM ENGINEER
Mar 8 - 14, 2010
Coal will continue to be a main source of the world's energy supply for years to come. New technologies are being developed to rid power generation of carbon dioxide in order to diminish environmental impact of greenhouse gas emissions.
Coal is becoming a favorite source of energy worldwide. The reasons for this are simple: growing population, and exploding demand for energy. In addition, many countries have substantial reserves of coal, making them independent of energy production.
The coal market is characterized by a very stable price structure. While prices for crude oil and natural gas have doubled in the past three years, the price of hard coal has increased by only around 20 percent during this period. However, CO2 emissions from coal-fired power plants are almost twice high those produced by combined cycle power plants (gas and oil).
GASIFICATION OF COAL
Gasification is the conversion of solid and liquid materials (e.g. coal or oil) into gas major components of which are hydrogen (H2) and carbon monoxide (CO). Gasification has been in practice for over a hundred years with the gas produced during the process used for meeting various needs such as domestic heating and lighting, as well as chemicals manufacturing e.g. ammonia (NH3) or methanol, and the production of petrol- and diesel-substitutes.
In recent years, there has developed interest in gasification to generate electricity. The initial reason for this was the development of large, efficient gas turbines. It was soon realized that the gasification of coal could potentially generate power as efficiently as the most modern coal-fired power plant does, but with much lower emissions.
The first experimental integrated gasification combined cycle (IGCC) power plant was built in the early 1970s in Germany, and today there are several coal-fired demonstration plants worldwide.
IGCC power plant can also be fired with oil-derived feedstock such as heavy oils and tars. These products are formed during oil-refining processes. Traditionally, these products have been used to manufacture heavy fuel oils for use in power station boilers and as marine fuel. However, the market for heavy fuel oil has declined rapidly in recent years, and some refineries now have a surplus of such products. Gasifying these heavy oils can provide H2, which can be used within the refinery to upgrade and clean other products including diesel and petrol.
There are at least four major oil IGCC projects active in Europe. Both biomass and wastes can be gasified. However, IGCC technology tends to favor large, centralized power plant whilst biomass and wastes are best exploited using smaller plant close to their source. An alternative, therefore, is to gasify the biomass or waste in a small gasifier adjacent to an existing power plant and use the gas produced to partially replace the coal or oil.
This allows an existing power station to utilize biomass and wastes as and when they are available. Some gasifier technologies allow biomass and wastes to be co-gasified with coal. Several biomass and waste gasification projects are mostly operational in Europe, with several of the most important in the UK. IGCC plants are still at the demonstration stage and need government support. The technology has three major deficiencies that need to be removed before it becomes widely used.
CHARACTERISTICS OF GASIFICATION
Gasification is the conversion of a carbon-containing solid or liquid substance into gas in which the major components are H2 (hydrogen) and CO (carbon monoxide). This gas can be used as fuel or chemical feedstock from which products such as NH3 or methanol can be manufactured. The defining chemical characteristic of gasification entails the partial oxidation of the feed material in combustion. The feed is fully oxidized whilst in pyrolysis the feed undergoes thermal degradation in the absence of O2. The oxidants for gasification are O2 or air and usually steam.
Steam acts as a temperature moderator, as the reaction of steam with the carbon in the feed is endothermic i.e. it absorbs heat. The choice of air or pure O2 depends on a number of factors such as the reactivity of the feed material, the purpose for which the gas is to be used, and the type of gasifier.
The initial application of gasification was to convert coal into a fuel-gas for domestic lighting and heating. Gradually, this application thinned out in most places of the world due to availability of natural gas, although gasification is still used for this purpose in China (and until recently in Eastern Europe). For the last few decades, the main application of gasification has been in the petrochemical industry to convert various hydrocarbon streams into 'synthesis gas' e.g. for manufacturing of methanol, the supply of H2 for NH3 production or the hydro desulphurization or hydro cracking of oil streams. Besides, specialized uses of gasification include conversion of coal into synthetic motor fuels (as practiced in South Africa) and for manufacturing substitute natural gas (SNG)- not practiced commercially at present but given serious consideration.
CTL POLYGENERATION CONCEPT
CTL (coal to liquid) plant configured to produce electric power and liquid fuels can readily be modified to a future generation power plant that can produce hydrogen, which can be utilized as a fuel. Hydrogen Fuel Cell uses hydrogen as its fuel and oxygen (usually from air) as its oxidant.
World over, the crude oil prices are becoming uncertain and more volatile. Many developed countries are enduring fiscal deficits. Possessing coal resources countries are keen of adopting CTL technology. China and India are ahead in the race to generate power from coal. A large CTL plant can produce electricity, LPG, light naphtha and diesel.
Pakistan is amongst the top four coal-rich countries in the world. Usually, governments are used to adopt technology that developed countries cannot even think of. For example, Pakistan is ready to spend million of dollars on LNG terminal and rental power plants whilst a little less amount could be spent on coal power generation plant up to 1000 megawatt with tariff rate not more than Rs.4 per unit as compared to Rs17 per unit in case of RPP.
PAKISTAN'S FIRST COAL POWER PLANT IN NOVEMBER 2010
Pakistan planned to build a 544 megawatt clean coal energy project to be set up in Jamshoro, Sindh. It will be the first coal sequestration project in Pakistan implying clean coal energy with no emission, no carbon footprint. All emissions will be pumped back into the ground and used for industrial purposes. The $420 million project, which will use coal obtained from Lakhra, is estimated to take around 12 to 14 months for completion. The project involves 420 million dollars of investment. This amount covers the equipment, the installation and project costs to bring the project to completion, but it does not include cost of running the plant for five years. The project will produce facility of 544MW (per hour) production in 12 months. The facility is a little cheaper than thermal energy. The coal is local, but not from Thar. It's Lakhra coal. There are differences in coal quality of Thar and Lakhra.
The basic content of the coal will generate the necessary BTUs without the addition of any foreign coal. The plant would use 300 tones/day of local coal, mined from a designated area (800 acres) that would be sufficient for 5 years.
Lakhra's coal does not have high moisture content. It has high limestone content. The byproduct of the coal would produce cement blocks.
The output price would be between 5 cents per kilowatt to 9 cents per kilowatt (approx. Rs 7.5 per kilowatt). Around 300 tons per day of coal will be used to generate 544 MW/annum of electricity.
The cost is directly influenced by the cost of the fuel. Specific difficulties emerge when estimating the cost of the fuel, which directly impact the price of utilities such as electricity, steam gas, and thermal fluids.
INCREMENT IN ELECTRICITY TARIFFS SINCE JULY 2009
- In October power tariff was increased 4.4%
- In November it was increased by 1.6%
- In January 1st 2010, the increment was 12%.
In case of both LNG and RPP, the country needs to heavily rely on imported gas as well as machineries. What is the use of such investments that would keep the country net importer forever? Alternatively, harnessing of local reserves of coal would make a different position. Japan is also importer of fuels but it offsets the impact on balance of payment because of its indigenous resource of technology.
Pakistan imports 2.5 million tons of coal per annum for cement industry. The country has 185 billion tones of estimated coal reserves, which can be exploited to the economic well-being of the country. Coal can be a main source of low-cost electricity.
Coal the black gold is found in all the four provinces of Pakistan. Out of total reserves, 3.3 billion tons are in proven/measured category and about 11 billions are indicated reserves, the bulk of it is found in Sindh. The current total mine able reserves of coal are estimated at 2 billion tones (60 % of the measured reserves).
Pakistan has emerged as one of the leading country - seventh in the list of top 20 countries of the world - after the discovery of huge lignite coal resources in Sindh. The coal deposits of Pakistan are restricted to Paleocene and Eocene rock sequences.
COALMINES IN PAKISTAN
There are four major mines in the country with a huge deposit of coal spreading over a million acres.
- LAKHRA COLLIERIES, DISTRICT DADU SINDH
Location 176km north of Karachi Or 65km northwest of Hyderabad Coalfield Lakhra Coalfield Geological horizon Paleocene Type of coal Sub-bituminous to lignite Calorific values 2,570 to 4,260 kcal Leased area (two leases) 5,096.49 acres Total coal reserves 38.82 million tons
- DEGARI COLLIERIES, DISTRICT MASTANG (QUETTA) BALOCHISTAN
Location 35km southeast of Quetta Geological horizon Eocene Coalfield Degari-Sor-Range Type of Coal Sub-bituminous-A to high volatile B-bituminous Calorific values 4,830 to 6,060 kcal Working depth 1000 meters (deepest mine in Pakistan) Mining system Long wall system Leased area 4,779.17 hectares coal reserves 15.42 million tones
- SOR-RANGE COLLIERIES, QUETTA
Location 16km east of Quetta Coalfield Degari Sor Range Field Geological horizon Eocene Type of coal Sub-bituminous-A to high volatile B-bituminous Calorific values 4,930 to 6,100 kcal Mining method Long wall system Leased area 1,674 acres Coal reserves 12.95 million tones
- SHAHRIG COLLIERIES
Location 160km north-east of Quetta Coalfield Shahrig- Khost- Harnai Coalfield Geological horizon Eocene Type of coal Sub Bituminous B to heavy volatile Bituminous-A Calorific values 4,420 to 7,000 kcal Mining method Long wall system Leased area 6,551.46 acres Coal resources 28.97 million tones
COAL DEPOSITS OF SINDH WITH SPECIAL REFERENCE TO HEAVY AND TRACE METAL IN THAR, SONDA, AND METING-JHIMPIR COALFIELD
Recently, huge coal deposits are explored in the Sindh province and further exploration is underway. The coal deposits have occurred so far in Thar, Sonda, Meting-Jhimpirm and Lakhra coalfields. These coal deposits occur in Bara Formation and in the Sonhari member of the Early Eocene Laki Formation. The Thar coalfield is the largest coalfield of the country and is situated in the district Tharparkar of southeast Sindh. It has the estimated resources of 175 billion tones. Coal in the Thar coalfield is present in the Bara Formation of Paleocene-Eocene age. The Sonda coalfield is located in the deltaic area of lower Indus and is lying in the east and northeast of Keenjhar lake in District Thatta. Coal seams in the Sonda coalfield occur in the Bara Formation of Paleocene age and the Laki Formation of Eocene age. The total resources of 280 million tones of coal have been explored in the Sonda coalfield. The Meting-Jhimpir coalfield in the District Thatta is the second oldest coalfield after Lakhra explored in Sindh. It is present in the Sonhari Member of the Laki Formation of Early Eocene age. About 161 million tones of coal resources are present in the Meting-Jhimpir coalfield.
There is great potential for exploration of coal deposits in the lower Indus Basin. Among the recently explored coal deposits in the province, the Thar Sonda and Meting-Jhimpir coalfields are of greater importance because these coal deposits can be exploited and utilized in the power generation plants and in other industries. Recently, a study was conducted to investigate the geological and geochemical characterization and environmental assessment of the Sindh coalfields before their use in various types of industries. The representative coal samples from the Sindh coalfields, especially Thar, Sonda, and Meting-Jhimpir have been investigated for the heavy, trace and light elements, the proximate and ultimate parameters, the combustion properties, the leaching behavior and the mineralogy by using various techniques.
THE FINDINGS WERE UNDER THE FOLLOWING.
- Average Pb contents are 34 ppm, 17 ppm and 23 ppm.
- Average Zn contents are 48 ppm, 44 ppm and 40 ppm.
- Average Cu contents are 18 ppm, 14 ppm and 22 ppm.
- Average Ni contents are 41 ppm, 34 ppm and 23 ppm.
- Average Cr contents are 20 ppm, 11 ppm and 12 ppm.
- Average Cd contents are 0.31 ppm, 0.27 ppm and 0.24 ppm.
- Average Co contents are 12 ppm, 83 ppm and 0.25 ppm.
- Average Fe contents are 5008 ppm, 5867 ppm and 4500 ppm.
- Average Mn contents are 0.67 ppm, 0.27 ppm and 0.09 ppm.
The above average heavy minerals are present in the Thar, Sonda and Meting-Jhimpir coalfields.
LIGHT ELEMENTS WITH THE COALS INCLUDE:
- Average amounts of Ca are 250 ppm, 203 ppm and 241 ppm.
- Mg are 76 ppm, 43 ppm and 60 ppm.
- Mg are 76 ppm, 43 ppm and 60 ppm.
- K are 210 ppm, 289 ppm and 252 ppm.
PROXIMATE PARAMETERS ARE:
- Average contents of fixed carbon are 40.44%, 41.20% and 40.11% and ash contents are 5 (165%, 5.77% and 10.77% in the Thar, Sonda and Meting-Jhimpir coalfields, respectively).
ULTIMATE PARAMETERS ARE:
- Average contents of hydrogen are 6.89%, 6.90%, and 6.82%.
- Average carbon contents are 62.10%, 61.43% and 60.20%.
- Average nitrogen contents are 0.35%, 0.31% and 0.32%.
- Average sulfur contents are 1.17%, 4.33% and 3.65 %.
The average calorific values for Thar, Sonda and Meting-Jhimpir coalfields are calculated as 10111btu/lb, 10301btu/lb and 10143 btu/lb respectively.
Comparison of the heavy and trace elements of Sindh coals with the other coals of Pakistan and elsewhere in the world shows that Sindh coals are relatively enriched in the Pb, Zn, Ni, Co and Fe. The amounts of fixed carbon, ash hydrogen, carbon and nitrogen in Sindh coals are within the permissible limit, however, the sulfur contents, especially in the Sonda and Meting-Jhimpir coals are above the permissible limit.
Most of the countries are looking for alternative ways of energy supply and Pakistan is still dependent on gas and oil for energy generation. Whether it is this government or pervious, the focus has been on churning out money from power plants regardless of the economic servility that enhances under the commercial and foreign dictates of energy production such as through rental power plants. No concrete efforts have been made so far to activate industrialization in the energy sector.
OTHER VALUABLE MATERIALS ASSOCIATED WITH PAKISTAN'S COAL
Mineralogical the Sindh coals contain quartz and kaolinite as the dominant mineral phases with subordinate amount of calcite, dolomite, muscovite, illite and pyrite. The quartz and muscovite are generally detrital and the remaining phases are authigenic. The sequential leaching analyses suggest that most of the heavy and trace elements are associated with HCI - soluble compounds and also with the insoluble or organic shielded matters. However, the Fe is generally associated with the HNO3 - soluble disulfides. The leaching behavior of the Sindh coal suggests that there are chances of contamination of the underground water system due to acid mine drain water during the large scale coal mining in the region. The combustion of the Sindh coals may also pose threat to the environment of the region as far as the S, Pb, Zn and Ni contents of Sonda and Meting-Jhimpir coals are concerned. These coals, therefore need to be cleaned and also the particulate emission level of the power generation plants should be substantially reduced before the use of these coals in power generation plants and other industries of Pakistan.
Carbon dioxide emission is the major problem with the coal fired power plant. Methodology was developed with Carbon Capture Sequestration (CCS) technology. The main principles of this technology are to absorb carbon dioxide from the flare gas.
Around 40 % of the world's power is generated in coal-fired power plants-and in China the figure is over 70 %. In 2006 in China alone, 174 coal-fired power plants in the 500 MW-class were connected to the grid. If conditions around the world don't change, the International Energy Agency (IEA) estimates that global consumption of coal will increase by 73 % between 2005 and 2030. That means that it is now more essential than ever for utilities, as well as the companies that build power plants, to design and operate coal-fired plants in the most environmentally friendly way possible.
With the oxy-fuel concept, instead of using air-as in conventional steam power plants-coal is burned with pure oxygen. This prevents large amounts of nitrogen, which makes up three-quarters of the volume of atmospheric air, from being needlessly added to the process and then forming nitrogen oxides during combustion. The flue gas produced is composed mostly of carbon dioxide and water vapor. By simply cooling and condensing the water, the CO2 can then be separated.
Siemens is working on different types of gasifier to absorb the maximum percentage of CO2. Furthermore, this CO2 can be used for manufacturing of ammonia, methanol, and dimethyl ether (DME), as well as fuels such as diesel and synthetic natural gas which are the major source of energy.
Fuel gasification takes place in a cylindrical reaction chamber at temperatures above the coal-ash fusion temperature. Finely-ground fuel is introduced with a mixture of oxygen, and steam if required, via a burner at the head of the reactor. Within a few seconds the mixture is converted into raw syngas consisting mainly of CO, H2, CO2, and H2O. Part of the liquid clinker solidifies on the cooled wall of the reaction chamber and thus forms a protective coating. In the quenching chamber, underneath the reaction chamber, syngas and liquid clinker are cooled by water injection. Solidified clinker granules are removed via a material lock at the foot of the quenching chamber.
China achieved much of its industrialization through utilization of demotic resources. Economists say that the energy demand over the next 5 years is expected to grow at a rate of 7.4 % per annum. It may be noted that in India the share of coal is as high as 54.5% in the total energy mix. To meet the future requirements of the country with indigenous resources, domestic exploration would have to be intensified to increase the share of coal to 25% in energy mix by 2020.