TURNING COAL IN TO LIQUID WITHOUT CARBON EMISSION
S.K.ANSARI (CHEMICAL ENGINEER)
SEEMA ANSARI (TELECOM. ENGINEER)
Mar 15 - 21, 2010
Pakistan has abundant natural resources including minerals, freshwater, soil rich for agriculture cultivation. Iran is taking full advantage out of unexploited crude oil reserves of Balochistan. Geographical survey shows the slope of crude oil tends toward the Balochistan but it is difficult to drill the mountainous rocks in the province.
Similarly coal are available in all the four provinces in the category of sub-bituminous further sub categories in A, B, and C which are ideal for electricity power plant. Although Pakistan has about 850 billion cubic feet resources of coal but unfortunately the country has been facing an acute shortage of electricity which is badly affecting the national economy.
The available resources of the coal are equal to 400 billion barrels of oil. The government spends over $4 billion annually to fulfill the demand of oil whilst it can meet the entire energy demand by utilizing only two percent of available resources of coal in the country.
Pakistan can produce 20,000 megawatts electricity for 40 long years by coals. The presence of coal deposits in Pakistan was known before independence, but its economic value was highlighted in 1980 when large reserves of coal were discovered in the Lakhra and Sonda areas of Sindh Province. The discovery of another huge coal deposit of 175.5 billion tonnes in an area of 10,000 sq. km in Tharparkar District of Sindh provided a quantum increase in the coal resources of Pakistan. After this discovery, Pakistan is now the 6th richest nation of the world as regards to coal resources. Pakistan did not appear even on the list of coal-rich countries before the discovery of Thar Coal.
Coal resources available to Pakistan exist in all four provinces and in AJK. The total coal reserves are estimated at 185.5 billion tonnes.
PAKISTAN COAL RESOURCES
SINDH Thar 175,506 6,244 - 11,045 Lakhra 1,328 5,503 - 9,158 Sonda - Jherrick 5,523 5,219 - 13,555 Meting - Jhimpir 473 5,219 - 8,660 Indus East 1,777 7,782 - 8,660 Badin 16 11,415 - 11,521 Sub - Total 184,623 . BALOCHISTAN Sor - Range / Degari 50 11,245 - 13,900 Khost - Sharigh - Harnai - Ziarat 88 9,637 - 15,499 Mach 23 11,110 - 12,937 Duki 56 10,131- 14,357 Sub - Total 217 . PUNJAB Salt Range 213 9,472 - 15,801 Makarwal 22 10,688 - 14,029 NWFP Hangu 82 10,500 - 14,149 Cherut 9 9,386 - 14,217 Sub - Total 91 . AZAD KASHMIR Koth 9 7,336 - 12,338 Grand Total 185,175 .
KINDS OF COAL
* Sub-bituminous coal
* Bituminous coal
AVERAGE EFFECTIVE CALORIFIC VALUES OF DIFFERENT FUELS
FUEL MOISTURE CONTENT IN DRY MATTER IN OPERATION BULK DENSITY EFFECTIVE CALORIFIC VALUE AT OPERATING MOISTURE CONTENT . % kg/m3 MJ/kg Btu/lb GJ/m3 Peat briquettes 15 750 17.0 7,310 12.0 Peat pellets 15 750 17.0 7,310 12.0 Peat pellets 30 550 14.0 6,020 7.7 Milled peat 45 350 10.5 4,515 3.7 Sod peat 35 350 12.8 5,504 4.5 Crushed coal 9 800 25.0 10,750 20.0 Anthracite 5 870 29.3 12,599 25.4 Heavy fuel oil - 950 40.6 17,458 39.0 Light fuel oil - 950 42.7 18,361 41.0 1 MJ/kg = 239 Kcal/kg
1 MJ/kg = 430 Btu/lb
Peat, which is a very low quality coal, has been used as a form of energy for at least 2000 years. However, the large electric power plants are fuelled by peat. Peat appears especially competitive in the 60-200 MW power plants, which necessitate the reclamation of vast areas of peat for large-scale peat extraction particularly in Ireland, Finland and the USSR.
Specialized technology was developed for these reclamation efforts. Peat is also used for electricity generation in small units in the range of 20-1 000 kW.
In Pakistan, coal is in the upper slab which is known as Sub-bituminous and is far better for electricity generation with low emission of CO2.
Thar maximum coal reserves fall in the category of high-class peat, which can be easily used for gasification and power generation. Thar coalís analysis reveals it consists of carbon (56.0%), hydrogen (5.2%), and Ash (6.0%).
GASIFICATION UNIT IN COAL POWER PLANT
United States or European countries are adopting coal as a raw material for power generations, even in china almost all power are generated by coal. World coal reserves report published in 2006 showed that by the end of 2006 the reserves would be as follows:
a) Bituminous & Anthracite coal 478,771 million tonnes
b) Sub-Bituminous & Lignite coal 490,293 million tones
The above figures did not include coal reserves of lignite in the Thar discovered later, and, which gave rise to global reserves by 185 billion tons.
COAL FIRED POWER GENERATION
Over half of the electricity generated in the US comes from coal-fired power plants, which are the largest source of greenhouse gases. Coal-fired power plants emit 66% of sulfur oxides (or acid rain), 40% of carbon dioxide (CO2), 33% of mercury and 22% of nitrogen oxides. Coal is the most CO2-intensive fossil fuel, emitting about 3 pounds of CO2 for every pound of coal burned. The US burns over 1 billion tons of coal every year. There are 492 coal power plants in the US with an average size of 667 megawatts (MW) and an average age of 40 years.
One 500 MW coal-fired power plant produces about 3 million tons/year of CO2. If 60% of the CO2 from all these plants are captured and compressed to a liquid for underground injection, its volume would be equal to the US oil consumption of 20 million barrels/day. A large coal-fired power plant emits the CO2 equivalent from one million SUVs. Therefore 500 MW coal fire powered produces 3 million tons/year of CO2. 172.8MT/hr of coal generates 3 million tons of CO2 per year.
CARBON CAPTURE POWER PLANT
There is an emission of CO2 from coal gasification. The emission of CO2 pollutes environment at the rate of 248.32 ton/hr or 3 million tons/year. Devices can absorb the CO2 however. Carbon Capture Sequestration absorbs the CO2 from the flue gas. Acid rains which are accompanied with nitrogen (78%) and which also burden to gasification can be illuminated if we supply only oxygen for gasification through Air Separating Unit.
The maximum output of carbon of crude oil is estimated at 40 MMbbl/year of oil over 15 to 20 years. Making an assumption based on the 20 years case, the oil resultant from storing 1.22 MM tons of CO2 is 2.0MMbbl/year, an average.
The composition of typical crude can be used to calculate the carbon recovered in the form of oil. For example a Middle Eastern heavy crude is composed of approximately 85 wt% carbon, 12 wt% hydrogen and 3wt% sulphur. For lighter crude, the hydrogen content will be higher and the sulphur content lower; yet the carbon content will remain essentially the same.
CARBON DIOXIDE SEPARATION FROM THE FLUE GAS IN GASIFICATION
The main problem with the gasification is the emission of carbon dioxide, but still many technologies come across to resolve this problem. The main aim is to collect the carbon dioxide from the flue gas and recycle it with the normal process
Scientists are working on such devices and they have already introduced a coal gasifier which can absorb up to 99.1% of carbon dioxide from the flue gas.
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. In order to cut CO2 emissions, it is necessary to increase the efficiency of existing and new power plants on one hand, and to separate carbon dioxide from power plant emissions and reliably sequester it on the other.
For several years now, ambitious efforts have been under way worldwide to realize what is called Carbon Capture and Storage (CCS) technology. There are three distinct methods of separating carbon dioxide from other gases generated by the combustion of coal:
- Coal gasification in Integrated Gasification Combined Cycle (IGCC) plants with separation before the combustion stage (pre-combustion capture),
- Separation of the CO2 from the flue gas beyond a conventional steam power plant (post-combustion capture),
- And the oxy fuel-process intended for steam power plants.
The term oxyfuel process means that the coal will burn in oxygen rather than air. 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. In developing the technology, Siemens has focused on the first two approaches, that is, pre- and post-combustion CO2 capture. There are big differences in the current stage of technological development of the three methods. Only the IGCC technology has so far been adequately tested, and there are numerous application examples of CO2 separation from syngas in the gas-processing industry or power plant.
High oil and gas prices have lead to a resurgence of coal as an affordable energy source. Especially coal-rich regions have increasingly been tapping their local resources. This allows them to reduce their reliance on foreign imports of natural resources and at the same time achieving stable prices to meet ever-growing energy demands. Gasification offers one of the cleanest and most flexible ways of converting coal and low-grade fuels into high-value products - electricity, chemicals or synthetic fuels. Combining gasification with advanced gas turbines in IGCC power plants results in a highly efficient technology for coal-based power generation.
Noxious components such as particulates sulfur and nitrogen compounds, which are typical of gasification, are removed by conventional gas treatment and conditioning processes downstream the gasification process.
MAIN FEATURES OF FUEL GASIFICATION TECHNOLOGY
- Dry solids feeding for high efficiency and low O2 consumption
- Top-mounted dust burner with extended burner lifetime
- Cooling screen for high availability and low maintenance
- Full water quench for simple and reliable design
BENEFITS OF FUEL GASIFIER
I. Feedstock flexibility: Suitable for all kind of coal types, especially lignite, biomass, petcoke and liquid refinery residues.
II. High carbon conversion: more than 98 %.
III. Operating pressures: 40 bar and above.
IV. Shorter start-up times.
V. Smaller dimensions for reduced equipment costs.
VI. High availability and low maintenance
VII. Proven experience: More than 20 years of successful operating technology.
Pakistan should go for IGCC technology, especially in volatile markets, coal can be a stable economic alter native. Taking the development of the prices for oil and gas into consideration, projects with integrated gasification of coal, coal to liquids, as well as coal to chemicals can become more attractive technological options in future.
China and European countries move at full steam on coal conversion project. With oil prices at historic highs, China and European countries including United States are moving full steam ahead with a controversial process to turn their vast coal reservoir in to barrels of oil and generating coal fire power.
The possibility of obtaining oil from coal is enticing to coal-rich countries including Pakistan. How long the world's oil reserves can continue to meet the energy demand?
The United States, Australia, India, and China are amongst countries looking for different technologies from coal but are constrained by environmental concerns associated with the process, which releases excessive amount of carbon gases and consumes huge quantity of water.
In China at Shenhua coal liquefaction plant will start operating later this year and is expected to convert 3.5 million tones of coal per year into 1 million tones of oil products. This is equivalent of about 20,000 barrels a day, which is a tiny percentage of China's oil needs as oil consumption in China is around 7.2 million barrels a day. According to the Chinese government, although it is a very small quantity they are producing from coal they had taken the starts with the coal technology.
Chinese hope that the coal technology will propel development while contributing to their plan to have 50 million tones of CTL and CTP by 2020 that would be about 286,000 barrels a day about four (4) percent of China's needs.
The relative low cost of CTL produced oil given current oil prices plus the chance to be more energy self-sufficient is a powerful incentive. Coal technology enthusiasts seek to find a way to turn coal into liquid without releasing CO2.
Two Chinese CLT projects will be able to produce 80,000 barrels per day or 3.4 million tons annually of diesel, naphtha, liquefied petroleum gas and jet fuel. Total cost was estimated at U$5 to 7 billion.