Environmental Impact: Rampal Coal Power Plant & Technology for Air Quality Improvemen

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G Mazumder and Saiful Huque

Today’s most important concern for our country is power generation. The Government of Bangladesh is sourcing for every possible solution to meet the power crisis. In recent years coal fired power plant is being heavily discussed. Like other Asian countries Bangladesh also wants to find a way to Energy solvency through Coal fired Power Plants, Nuclear Power Plants and Renewable Energy Sources.

 

The Bangladesh Government planned for a 1320 megawatt coal-fired power station at Rampal Upazila of Bagerhat District in Khulna. This work is proposed as a joint partnership between India’s state owned National Thermal Power Corporation and Bangladesh Power Development Board. The joint venture company is known as Bangladesh India Friendship Power Company (BIFPC). The proposed project, on an area of over 1834 acres of land, is situated 14 kilometers north of the world’s largest mangrove forest ‘Sundarbans’ which is a UNESCO world heritage site. It will be the country’s largest power plant.

 

Coal fired Rampal power plant planning is considered to be one of the most controversial decisions as this project has environmental issues. However the government of Bangladesh rejected allegations that the coal-based power plant would adversely affect the world’s largest mangrove forest. The energy advisor of the prime minister said that the controversy over the power plant and its impact on the Sundarbans was “not based on facts”. He also said that the plant will not negatively affect the mangrove forest because the emission of greenhouse gas will be kept at a minimum level. The government also affirmed they will import high quality coal, build a 275 meter high chimney and employ state-of-the art technology to keep its impact on the Sundarbans at a negligible level.

 

The crucial discussion about environmental security of Sundarbans is not satisfied yet. Regarding this we tried to find out the natural capability of Sundarbans to face environmental changes after having the plant established for operation. We tried to figure out the approximate carbon emission of that power plant and calculated the tolerance level of Sundarbans by itself. Beside this we discussed about technologies which may actually secure Sundarbans from being destroyed.

 

How much Carbon Sundarbans will face daily?

Generally no power plant runs at their full capacity. Carbon emission depends on the amount of generation. To simplify our calculation we took an arbitrary generation profile for a typical day. Emissions also depend on quality of coal. There are several types of coal available in the international market which is popularly used in coal fired power plants. Below table shows the information of such categories of coal and their properties. We calculated on Bituminous which releases least carbon.

 

Reference: [The source of this information is according to the Independent Statistics and analysis: U.S. Energy Information Administration, Last Updated: 17April2014, www.eia.gov]

Fuel CO2 emissions factor

(Lbs of CO2 per Million Btu)

Heat Rate

(Btu per kWh)

Lbs CO2 per kWh

(CO2 emissions factor×Heat Rate)/1000000

Bituminous 205.3 10,107 2.08
Sub-bituminous 212.7 10,107 2.16
 Lignite 215.4 10,107 2.18

 

We can calculate the amount of carbon dioxide (CO2) produced per kilo-watt-hour (kWh) for specific fuels and specific types of generators by multiplying the CO2 emissions factor (in pounds of CO2 per million Btu) by the heat rate of a generator (in Btu per kWh), and dividing the result by 1,000,000. Considering heatrate and carbon emission ratio bituminous can be an environmentally efficient choice as the primary fuel.

 

CO2 Emission in Million Kg = [(Output in MWh) × 1000 × {(CO2 emissions factor × Heat Rate) ÷1000000} × 0.453592] ÷ 1000000

 

Approximate Operation Profile for a Single day
Time Hour of Operation Percentage of Load over full  Capacity Generation in MW Output in MWh Output in KWh Co2 Produced in Lbs CO2 in Million Kg
6:00AM to 10:00AM 4 20% 264 1056 1056000 2196480 1.0
10:00AM to 02:00PM 4 80% 1056 4224 4224000 8785920 4.0
02:00PM to 03:00PM 1 30% 396 396 396000 823680 0.4
03:00PM to 6.00PM 3 80% 1056 3168 3168000 6589440 3.0
6:00PM to 10:00 PM 4 40% 528 2112 2112000 4392960 2.0
10:00PM to 12:00AM 2 20% 264 528 528000 1098240 0.5
12:00AM to 6:00AM 6 10% 132 792 792000 1647360 0.7
Total 24     12276 12276000 25534080 11.6

 

Now we need to know the amount of carbon in 11.6 MKg of CO2

  • 44 gm of CO2 = 1 mole
  • 1000 gm of CO2 = 1 mol/44g = 22.7 moles of C.
  • 1 Mole of C= 12 gm of C
  • 22.7 moles of C =22.7 x 12= 272.4 gm of C
  • 1kg of CO2 contains 272.4 gm of C = 0.2724 Kg of C
  • 11.6 Kg of CO2 contains =11.6V 14×”> 0.2724 = 3.15948 kg of C

[Molar mass of CO2 = 44 gm/mole, gram molar mass of C = 12]

 

 

So 11.6 Million Kg of CO2 contains 3.16 Million Kg of Carbon.

 

As of our approximate generation profile RAMPAL power plant will produce 3.16 million Kg Carbon for every 24 hours of operation. Now the question is how much carbon can be sequestrated by Sundarbans each day. Do we have any idea?

 

Natural Carbon Sequestration Ability of Sundarbans

Mangroves can sequestrate or take up more carbon than any other type of forest land. Because mangroves traps not only fine sediment and organic matter but also coarse sediment driven by storm waves. These form special mangrove sediment together. Sedimentation rate of mangrove is high. It also produces litter very quickly, which provides more carbon sequestrated in sediments of mangrove. This indicates high below ground carbon sequestration. Various components like area in km2, NPP, organic carbon export were estimated by many researchers for Global Carbon Mangrove Budget.

 

The global storage of carbon (C) in mangrove biomass is estimated at 4.03 Pg C. The average rate of wood production is 12.08 Mg ha–1yr–1, which is equivalent to a global estimate of 0.16 Pg C/yr stored in mangrove biomass. The net ecosystem production in mangroves is about 0.18 Pg C/yr23. It is estimated that mangroves sequester approximately 25.5 million tonnes of carbon every year. Mangroves sequester approximately 1.5 metric tons/hectare/yr of carbon or 3.7 lbs/acre/day of carbon (1336 lbs/acre/yr).

 

Reference: [J. Environ. Res. Develop. Journal of Environmental Research And Development Vol. 7 No. 1A, July-September 2012, CARBON SEQUESTRATION IN MANGROVES ECOSYSTEMS Patil V.*, Singh A., Naik N., Seema U. and Sawant B. National Institute of Industrial Engineering, NITIE, Mumbai ( INDIA)Received May 05,2012 Accepted August 20,2012]

 

The amount of carbon Sundarbans would be able to sequestrate per day can be calculated easily. The total area of Sundarbans is 10,000 km2. About60% of the land mass lies in Bangladesh and the rest is in India. The land area, including exposed sandbars, occupies 414,259 ha (70%) with water bodies covering 187,413 ha (30%).

 

Area in KM Sq Area in Acre Carbon Sequestration per acre in Lbs  in KG Sequestration Amount of C in KG in Million KG
10,000 2471050 3.7 1.7 4147139.5 4.1

 

So far we can conclude roughly that if we supply 4.1 million Kg of carbon di oxide daily, Sundarbans can absorb this easily. Actually there is some difference between absorption and sequestration. Sequestration is not only absorbing the carbon but sending it to the soil through ecological systems. The figure below can illustrate the concept more clearly.

 

The volume of approximate carbon emission from RAMPAL plant is very marginal with the ability of Sundarbans. We have only calculated on emissions but coal transportation also spread carbon and contaminates the environment. As Sundarbans is already contributing to sequestrate carbon from other sources, if sufficient safety measurements are not taken it may result destructions to this mangrove. The Government already says that State of art technology will be used. This statement may be elaborated by properly describing the planning and measurements. A chimney of 275 meter height will be built. This will be the country’s tallest structure. Only a taller chimney will not be able to solve the issue overnight. There are many disadvantages of using taller stock also. We will later discuss about this.

 

Climate of Sundarbans: Obstacle or Advantage?

As discussed earlier about carbon sequestration, there are some extra properties of this forest which can accelerate sequestration process like rainfall, tides. Saline water is also a good absorber of CO2. The forest is located in the South of the Tropic of Cancer and, at the northern limits of the Bay of Bengal, which may be classified as a tropical moist forest. Typically the rainfall occurs at monsoon. It is dry during November to April but rain shower lasts from May to October. Rainfall is relatively heavy with a mean of about 1700-mm per annum. Monthly rainfall varies from a dry season of a few millimeters in December to a wet season of about 600 mm in July. Both rainfall and temperature are sharply seasonal. The relative humidity IS 76% to 85%.

 

Higher Chimney & Wind Flow Characteristics of Sundarbans

It is studied that in Sundarbans region wind is generally light and blows from north to northwest between the months of October to April except during cyclonic storms. During the period of monsoon they are from the Southeast. At the time of cyclonic storm wind velocities can reach up to 120km/hour. The forests are exposed to the strong winds during March to September. Monsoon lasts between June and October. Cyclones could occur during the period of September to December as well.

 

Rainfall clears air effectively but this will not ensure a safer environment at all. Tides in the Bay of Bengal are semi-diurnal with a normal period of 12 hours 50 minutes that sweeps most part of the Sundarbans twice a day. But during the cyclonic storm, tidal waves can result in widespread inundation. Tidal waves move from the south to the north.

 

Stack height is one of the several factors that contribute to the interstate transport of air pollution. According to reports, tall stacks generally disperse pollutants over longer distances than shorter stacks and provide pollutants with more time to react in the atmosphere to form ozone or particulate matter. However, the interstate transport of air pollution is a complex process that involves several variables — such as total emissions from a stack, the temperature and velocity of the emissions, and weather — in addition to stack height. As it is prescribed to build a high chimney at Rampal power plants we may face this interstate transport of pollutants.

 

From October to April wind will come from north and northwest and will sweep the stack exhausts toward the Bay of Bengal. During monsoon exhausts will be driven towards Satkhira region as wind will flow from southeast corner. See figure: 3; Population of these areas will experience air pollution if this site is established for power generation. We have doubts that higher chimney may cause interstate pollution over a large area.

 

Pollution Control and State of Art Technology

If government is meant to establish state of art technology to minimize carbon emission then they must setup equipment which will filter the exhaust/flue to the tolerable level before being fed to the chimney. Figure 4 shows some pollutant control equipment used for the treatment of exhaust gas. Table shows how much improvement can be achieved through these methods. Importantly these are very costly equipments to be established as well as for maintenance.

 

 

Table: Summary of Pollution Control Equipment Used at Coal Power Plants

Pollutant Targeted Control Equipment Name How it works Removal Efficiency
Particulate Matter ESP(Electrostatic Precipitators) An induced electrical charge removes particles from flue gas Capable of 99.0-99.5% removal of particulates
Particulate Matter Fabric Filter(Commonly referred to as a ‘Baghouse’) Flue gas passes through a tightly woven fabric filter Capable of 99.9% removal of particulates
SO2 FGD(Flue Gas Desulphurization) unit (Commonly referred to as a ‘Scrubber’) Wet FGDs inject a liquid sorbent, such as limestone into the flue gas to form a wet solid which can be disposed of or dried.

 

Dry FGDs inject a dry sorbent, such as lime into the flue gas to form a solid by-product which can be collected

Wet FGDs- Capable of 80-99% removal of SO2,

Dry FGDs-Capable of 70-95% removal of SO2

NOX Combustion control technologies such as low-NOX burners Coal combustion conditions are adjusted so that less NOX formation occurs Capable of 40-45% reduction in the formation of NOX
NOx Post combustion controls, Such as SCR(Selective Catalytic Reduction) and SNCR (Selective Non Catalytic Reduction)units SCRs inject ammonia into flue gas to form nitrogen and water and use a catalyst to enhance the reaction

 

SCNRS inject ammonia as well, but do not use a catalyst

SCRs- Capable of 70-95% removal of NOX, SNCRs- Capable of 30-75% removal of NOX

 

Reference: [Report to the Chairman, Subcommittee on Oversight, Committee on Environment and Public Works, U.S. Senate May 2011 AIR QUALITY Information on Tall Smokestacks and Their Contribution to Interstate Transport of Air Pollution, GAO-11-473,United States Government Accountability Office, GAO]

 

Efficiency Improvement for Low Emission

If it is unavoidable that we have to establish a coal fired power plant in Rampal then we should build a very efficient one. An efficient power plant uses less coal, has lower emissions, and experiences lower variable costs. Taking efficiency improvement measures at power plants is an effective and economic way of reducing carbon dioxide (CO2) emissions. In reality efficiency is to be maintained throughout the life time of a plant. It is audited and rectified back for more efficiency improvement. For a typical pulverized coal–fired plant, a 1% increase in net unit efficiency results in a 2.7% reduction in CO2 emissions.

 

As this plant has severe environmental issue we have to make sure that we are running efficiently. Sometimes the term efficiency is described as heat rate. Improvements in heat rate reflect the improvement of efficiency. The table below lists the improvement options of heat rate. It also shows how far we can reduce carbon emission by improving different sections and part of a coalfired power plant.

 

Table: Options for Efficiency Improvement

Improvement Option Heat Rate Improvement (%) Comment
Thermal drying of high moisture coal 0.6 to 5.9 Depends on coal type
Use of heat recovered from flue gas 1.2 to 3.6 Depends on utilization of recovered heat
Improvements to steam turbine cycle 2 to 4.5  
Improvements to heat rejection system 0.5 to 3 Depends on unit Load
Improvement to boiler auxiliaries 0.2 to 1 Site Specific
Improvement to sensors and controls Up to 1.5 Depends on unit age
Balancing of coal flow Up to 1 Site Specific
Combustion optimization 1 to 2 Site Specific
Shoot-blowing Optimization 1 to 2 Site Specific

 

 

Coal Grade Rally Matters!

However, the degree of possible heat rate improvement largely depends on the type of coal burned. The most desirable heat rate improvement option for power plants burning high-moisture coals is to pursue coal-drying technologies using recovered low-grade heat from flue gas.

 

Reference and Source: [For more information concerning power plant heat-recovery technologies, see “Power 101: Flue Gas Heat Recovery in Power Plants,” Parts I, II, and III, in the POWER archives.]

 

There are many heat rate improvement options. In general, unit heat rate can be improved by improving boiler combustion efficiency and turbine cycle efficiency, and by reducing auxiliary power use. Note that heat rate improvements depend on many site-specific factors.

 

Reference: [Increasing Efficiency and Reducing Emissions of Existing Pulverized Coal-Fired Units, ICCI Project Number 07-1/5.1A-1]

 

Low-rank, high-moisture coals constitute about 50% of the U.S. and world coal reserves. Given the abundance of these low-cost coals, the use of high-moisture coal for power generation is common and growing. In the U.S. alone, 279 power facilities burn high-moisture coals, such as lignite and Powder River Basin sub-bituminous coal. When high-moisture coals are burned in utility boilers, about 7% of the fuel heat input is used to evaporate and superheat fuel moisture that leaves with the flue gas, with most of this loss associated with the latent heat of evaporation.

 

Furthermore, high-moisture, low heating value coals result in higher fuel and flue gas flow rates, higher auxiliary power use, higher net unit heat rate, and higher mill, coal pipe, and burner maintenance compared to bituminous coals. Conversely, a reduction in coal moisture content by thermal drying improves boiler and unit efficiency, plant operation, and economics — all the while reducing CO2 emissions. However, many of the coal-drying thermal processes developed so far are either mechanically complex or require costly primary energy or steam to remove moisture from the coal. This significantly increases fuel processing cost, which is the main barrier to industry acceptance.

 

So we have to use high grade coal to minimize the heat loss as well as the cost.

 

Advanced efficiency improvement Technologies for coal-fired power plants

 

Fluidized Bed Combustion: Fluidized Bed Combustion (FBC) is a very flexible method of electricity production — most combustible material can be burnt including coal, biomass and general waste. FBC systems improve the environmental impact of coal-based electricity, reducing SOx and NOx emissions by 90%. In fluidized bed combustion, coal is burned in a reactor comprised of a bed through which gas is fed to keep the fuel in a turbulent state. This improves combustion, heat transfer and recovery of waste products. The higher heat exchanger efficiencies and better mixing of FBC systems allow them to operate at lower temperatures than conventional pulverized coal combustion (PCC) systems. By elevating pressures within a bed, a high-pressure gas stream can be used to drive a gas turbine, generating electricity. FBC systems fit into two groups, non-pressurized systems (FBC) and pressurized systems (PFBC), and two subgroups, circulating or bubbling fluidized bed.

 

Non-pressurized FBC systems operate at atmospheric pressure and are the most widely applied type of FBC. They have efficiencies similar to PCC — 30-40% Pressurized FBC systems operate at elevated pressures and produce a high-pressure gas stream that can drive a gas turbine, creating a more efficient combined cycle system — (over 40%). Bubbling uses a low fluidizing velocity — so that the particles are held mainly in a bed — and is generally used with small plants offering a non-pressurized efficiency of around 30%. Circulating uses a higher fluidizing velocity — so the particles are constantly held in the flue gases — and are used for much larger plant offering efficiency of over 40%. The flexibility of FBC systems allows them to utilize abandoned coal waste that previously would not be used due to its poor quality.

 

Supercritical & Ultra supercritical Technology: New pulverized coal combustion systems — utilizing supercritical and ultra-supercritical technology — operate at increasingly higher temperatures and pressures and therefore achieve higher efficiencies than conventional PCC units and significant CO2 reductions. Supercritical steam cycle technology has been used for decades and is becoming the system of choice for new commercial coal-fired plants in many countries. Research and development is under way for ultra-supercritical units operating at even higher efficiencies, potentially up to around 50%. The introduction of ultra-supercritical technology has been driven over recent years in countries such as Denmark, Germany and Japan, in order to achieve improved plant efficiencies and reduce fuel costs. Research is focusing on the development of new steels for boiler tubes and on high alloy steels that minimize corrosion. These developments are expected to result in a dramatic increase in the number of SC plants and USC units installed over coming years.

 

Pulverized coal combustion systems: Producing electricity in coal power plants can take place in a number of ways with varying degrees of efficiency. In conventional coal-fired plants coal is first pulverized into a fine powder and then combusted at temperatures of between 13000C to 17000C. This process heats water in tubes in the boiler so that it becomes steam at a pressure of around 180 bars and a temperature of 5400C. This steam is passed into a turbine to produce electricity (see Figure 1). Pulverized coal power plants account for about 97% of the world’s coal-fired capacity (IEA 2008, p. 225). The average net efficiency (energy produced minus energy used within the plant) is around 35%, which means that 35% of the energy in one unit of coal is transferred into electricity. Pulverized coal power plants can have a size of up to 1000 MW and are commercially available worldwide.

 

Pulverized coal power plants account for about 97% of the world’s coal-fired capacity. The conventional types of this technology have an efficiency of around 35%. For a higher efficiency of the technology supercritical and ultra-supercritical coal-fired technologies have been developed. These technologies can combust pulverized coal and produce steam at higher temperatures and under a higher pressure, so that an efficiency level of 45% can be reached (ultra-supercritical plants). Supercritical power plants have become the system of choice in most industrialized countries, while ultra-supercritical plant technology is still in the process of demonstration. Supercritical and ultra-supercritical plants are more expensive (because of the higher requirements to the steel needed to stand the higher pressure and temperature) but the higher efficiency results in cost savings during the technical lifetime of the plants. The emissions of CO2 per MWh delivered to the grid could reduce from 830 kg to 730 kg.

 

Integrated Gasification Combined Cycle (IGCC): An alternative to achieve efficiency improvements in conventional pulverized coal-fired power stations is through the use of gasification technology. IGCC plants use a gasifier to convert coal (or other carbon-based materials) to syngas, which drives a combined cycle turbine. Coal is combined with oxygen and steam in the gasifier to produce the syngas, which is mainly H2 and carbon monoxide (CO). The gas is then cleaned to remove impurities, such as sulphur, and the syngas is used in a gas turbine to produce electricity. Waste heat from the gas turbine is recovered to create steam which drives a steam turbine, producing more electricity hence a combined cycle system.

 

In an IGCC plant an additional ‘shift’ reaction can produce hydrogen and the CO can be converted to CO2 which can then be captured and stored. There are some challenges in IGCC development and commercialization. Reliability, availability and cost are big issues for the wider uptake of IGCC as they are significantly more expensive than conventional coal-fired plant. Gasification may also be one of the best ways to produce clean-burning hydrogen for tomorrow’s cars and power-generating fuel cells. Hydrogen and other coal gases can be used to fuel power-generating turbines, or as the chemical building blocks for a wide range of commercial products, including diesel and other transport fuels.

 

CCS

Carbon Capture and Storage (CCS) is a technology that can capture up to 90% of the carbon dioxide (CO2) emissions produced from the use of fossil fuels in electricity generation and industrial processes, preventing the carbon dioxide from entering the atmosphere. Furthermore, the use of CCS with renewable biomass is one of the few carbon abatement technologies that can be used in a ‘carbon-negative’ mode actually taking carbon dioxide out of the atmosphere. The CCS chain consists of three parts; capturing the carbon dioxide, transporting the carbon dioxide, and securely storing the carbon dioxide emissions, underground in depleted oil and gas fields or deep saline aquifer formations. First, capture technologies allow the separation of carbon dioxide from gases produced in electricity generation and industrial processes by one of three methods: pre-combustion capture, post-combustion capture and oxy-fuel combustion. Carbon dioxide is then transported by pipeline or by ship for safe storage. Millions of tonnes of carbon dioxide are already transported annually for commercial purposes by road tanker, ship and pipelines. The U.S. has four decades of experience of transporting carbon dioxide by pipeline for enhanced oil recovery projects.

 

 

 

The carbon dioxide is then stored in carefully selected geological rock formations that are typically located several kilometers below the earth’s surface. At every point in the CCS chain, from production to storage, industry has at its disposal a number of process technologies that are well understood and have excellent health and safety records. The commercial deployment of CCS will involve the widespread adoption of these CCS techniques, combined with robust monitoring techniques and Government regulation.

 

What to Ensure

In fact Sundarbans supports and holds wide range of variety of life and nature inside it. We cannot leave any Environment issues untreated to alter its ecosystem. It is true that we need power and power plants will accelerate our economy. If we have to establish a coal based power generation unit over there then we must contemplate on it to make sure that it is safe. Also we have to have a clear knowledge of how much safe we are. In this write-up we tried to find the approximate amount of carbon emission for a day on the basis of an arbitrary generation profile. We discussed about advanced technologies which are being used in many countries for environment protection. We have talked about pollution control and advanced coal firing technologies also. If we want to minimize carbon emission to zero level we may choose CCS technology. As the Sundarbans is near the Bay of Bengal we will get an advantage on carbon carriage. CCS can remove 90% of the carbon dioxide (CO2) emissions produced. And if we use some pollutant control technology along with CCS we may be able to expect a clean Sundarbans as it is today. We need to know that coal transportation also pollutes environment. There are also many advanced carrying systems to protect environment.

 

Establishing a clean power plant involves cost, however it is not invaluable as the Sundarbans. First we have to find out how much we need to spend for clean generation. Then we need to calculate whether these costs are recoverable through payback period or not. If we are able to ensure a safe coal fired power plant to its tolerance level, only then may we think of it. Otherwise it will be too dangerous for us as well as for the world’s largest mangrove forest.