performance investigation of existing commercial

National Conference on Physics Research and Education in Bangladesh, 24-25 April, 2015 Atomic Energy Centre, Dhaka

BANGLADESH PHYSICAL SOCIETY

PERFORMANCE INVESTIGATION OF EXISTING COMMERCIAL GASIFIER AND COAL GASIFICATION PROSPECTS IN BANGLADESH Md. Kamruzzaman1, Dr. Md. Raju Ahmed2 1

Master’s Student, 2Associate Professor

Department of Electrical & Electronic Engineering, Dhaka University of Engineering and Technology (DUET), Gazipur, Bangladesh 1

[email protected]

2

[email protected]

ABSTRACT Gasification is an emerging process that converts organic or fossil-based carbonaceous materials specially coal into syngas which contain basically carbon monoxide, hydrogen and carbon dioxide and this syngas is itself a fuel. This is achieved by reacting the material at high temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam. Gasifier (gasification reactors) is the heart of gasification process. Different in design and operational characteristics, there are various types of gasifiers employed commercially. Therefore, to setup a new gasification plant, performance of commercial gasifier is important issue to investigate. Commercial gasifiers of GE Energy, CB&I E-Gas™ and Shell SCGP are examples of entrainedflow types. Fixed-or moving-bed gasifiers include that of Lurgi and British Gas Lurgi (BGL). Examples of fluidized-bed gasifiers include the catalytic gasifier technology being commercialized by Great Point Energy and the Winkler gasifier. This paper investigates the performance of all types of commercial gasifier existing and makes a comparison among them. In addition, the setup cost for different types of gasifier plant is discussed here. Though many nations are moving to renewable energy sources, coal remains the most abundant fossil fuel on the planet; the worldwide scenario shows that around 61 percent of total proved reserve fuel is coal. Energy sector of Bangladesh is exceedingly depended on the limited gas reserve. Given the rising demand for fuel, it will be very difficult to meet this demand with only indigenous natural gas. About 80% of the power generation in the country is now gas based. Therefore diversification of fuel has become indispensible it has been envision 2021 that 53% of the power generation will be coal based by year 2021. Bangladesh is very lucky that it has significant but almost untapped high quality coal resource. Coal gasification technology can be empowered to generate electricity with high efficiency and low emission. In addition, this technology can reduce the dependency on natural gas. The paper gives an overview of the current state of coal scenario in Bangladesh and discusses the possible application of gasification technology in Bangladesh.

KEYWORDS Coal Gasification, Synthesis Gas, Commercial Gasifier, IGCC, Bangladesh

1. INTRODUCTION Coal gasification offers one of the most versatile and clean ways to convert coal into gas, hydrogen, and other valuable energy products. The production of synthetic gas from coal is an interesting opportunity for both exploiting coal and biomass, and for replacing oil products for transportation and other uses. Gasifier (gasification reactors) is the heart of gasification process. Different in design and operational characteristics, there are various types of gasifiers employed commercially. Therefore, to setup a new gasification plant, performance of commercial gasifier is important issue to investigate. Many organizations develop different types of gasifier commercially. Four gasification technologies have been proven at the large scale (>1250 tpd) needed for IGCC applications and some other are on developing stage. This section briefly discusses the 7 major gasifier concepts by providing a little the history of the development of each gasifier type and giving a general description as to the type of reactor each gasifier is, such as refractory lined, slurry fired, etc. Commercial gasifiers of GE Energy, CB&I E-Gas™ and Shell SCGP are examples of entrained-flow types. Fixed-or moving-bed gasifiers include that of Lurgi and British Gas Lurgi (BGL). Examples of fluidized-bed gasifiers include the catalytic gasifier technology being commercialized by Great Point Energy and the Winkler gasifier. This paper investigates the performance of all types of commercial gasifier(Large scale) existing and makes a comparison among them. The present energy crisis in Bangladesh is partly due to over-dependence on gas which fulfils more than 70 per cent of its energy needs. The present gas deficit against the national demand on a Paper No : E-IIB-3

Corresponding Author: Md. Kamruzzaman, Department of Electrical And Electronic Engineering (EEE) at Dhaka University of Engineering and Technology (DUET), Gazipur, Bangladesh.



daily basis is expected to increase further in the future. The crisis will deepen unless a greater share of indigenous coal is included in the energy mix. Coal gasification technology would be the best choice for Bangladesh to generate energy from coal without effecting environment. The prospects of coal gasification in Bangladesh are discussed in this paper. We also propose a coal gasification based energy infrastructure for Bangladesh. In this infrastructure coal is converted to syngas in a central gasification plant, then it purified through purification plant, then processed to make Synthesis Natural Gas (SNG), then it transmitted via dedicated pipeline or injected into existing natural gas pipeline to the different types of user like Household, Thermal Power Plant, Brick Field, Ceramics & Glass Industry and any kind of thermal process industry. This proposed technology will reduce the dependency on natural gas and help to build a sustainable energy plan for future.

2. COAL GASIFICATION Gasification is a process in which combustible materials are partially oxidized or partially combusted. The product of gasification is a combustible synthesis gas, or syngas. Because gasification involves the partial, rather than complete, oxidization of the feed, gasification processes operate in an oxygen-lean environment. As figure1 indicates, the stoichiometric oxygen-to-coal ratio for combustion is almost four times the stoichiometric oxygen-to-coal ratio for gasification of coal.

Fig. 1. Diagram showing the products of reaction as a function of oxygen-to-coal ratio ( Reprinted from M. Ramezan, “Coal-based Gasification Technologies: An Overview” NETL Gasification Technologies Training Course, Sept.2004.)

Just as most combustion-based processes such as power plants operate with excess oxygen to ensure complete conversion of the fuel, gasification processes also typically operate above their stoichiometric oxygen-to-fuel ratio to ensure near complete conversion to syngas. The amount of oxygen used in gasification, however, is always far less than that used in combustion and typically is less than half. In addition to coal, gasification processes can use petroleum coke, biomass, heavy oil, or even natural gas as the feedstock; however, this document will focus on coal gasification processes. As indicated in figure 1, the products of reaction change significantly as the oxygen-to-fuel ratio changes from combustion to gasification conditions. These changes are summarized in table 1. Because the mixture under gasifying conditions is fuel-rich, there are not enough oxygen atoms available to fully react with the feed. Consequently, instead of producing CO2, the carbon in the feed is converted primarily to CO, and the hydrogen in the fuel is converted mostly to H2 rather than H2O. Both CO and H2 are excellent fuels for use in a combustion turbine; however, their combustion characteristics are significantly different from natural gas. Table 1 Comparison of the primary products created by the main fuel constituents in combustion and gasification

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3. COAL GASIFIER Gasifier is the heart of gasification technology. Although there are various types of gasifers (gasification reactors), different in design and operational characteristics, there are three main gasifier classifications into which most of the commercially available gasifiers fall. These categories are as follows: Type of Commercial Gasifiers: A) Fixed-bed Gasifiers (Counter current): 1. Lurgi Dry-Ash Gasifier 2. British Gas/Lurgi Gasifier B) Fluidized-bed Gasifiers: 1. KBR Transport Gasifiers 2. Great Point Energy 3. High Temperature Winkler (HTW) Gasifier 4. U-GAS Gasifier 5. ICC/CAS AFB Gasifier

C) Entrained-flow Gasifiers: 1. GE Energy (Chevron Texaco) Gasifier 2. CB&I E-Gas™ Gasifiers 3. Shell Gasifiers 4. Siemens Gasifiers 5. PRENFLO Gasifier 6. MHI Gasifier 7. EAGLE 8. ECUST Gasifier 9. HCERI Gasifier 10. MCSG Gasifier 11. Tsinghua OSEF Gasifier

3.1 Generic Types of Gasifiers : Currently available gasifiers can be classified basically as three reactor types. The processes that require a high throughput capacity in a single reactor generally employ entrained-bed type, as in IGCC, since the reactor size can be minimized by fast residence time (typically less than 5 sec) in the gasifier as well as by high pressure. i) Moving Bed A diagram of a generic moving bed gasifier is shown in figure 2(a). Moving bed gasifiers are counter current flow reactors in which the coal enters at the top of the reactor and air or oxygen enters at the bottom. As the coal slowly moves down through the reactor, it is gasified and the remaining ash drops out of the bottom of the reactor. Because of the counter current flow arrangement, the heat of reaction from the gasification reactions serves to pre-heat the coal before it enters the gasification reaction zone. Consequently, the temperature of the syngas exiting the gasifier is significantly lower than the temperature needed for complete conversion of the coal. The residence time of the coal within a moving bed gasifier may be on the order of hours. ii) Fluidized Bed A diagram of a generic fluidized bed gasifier is shown in figure 2(b). A fluidized bed gasifier is a back-mixed or well-stirred reactor in which there is a consistent mixture of new coal particles mixed in with older, partially gasified and fully gasified particles. The mixing also fosters uniform temperatures throughout the bed. The flow of gas into the reactor (oxidant, steam, recycled syngas) must be sufficient to float the coal particles within the bed but not so high as to entrained them out of the bed. However, as the particles are gasified, they will become smaller and lighter and will be entrained out of the reactor. It is also important that the temperatures within the bed are less than the initial ash fusion temperature of the coal to avoid particle agglomeration. Typically a cyclone downstream of the gasifier will capture the larger particles that are entrained out and these particles are recycled back to the bed. Overall, the residence time of coal particles in a fluidized bed gasifier is shorter than that of a moving bed gasifier. iii) Entrained Flow A diagram of a generic entrained flow gasifier is shown in figure 2(c). Finely-ground coal is injected in cocurrent flow with the oxidant. The coal rapidly heats up and reacts with the oxidant. The residence time of an entrained flow gasifier is on the order of seconds or tens of seconds. Because of the short residence time, entrained flow gasifiers must operate at high temperatures to achieve high carbon conversion. Consequently, most entrained flow gasifiers use oxygen rather than air and operate above the slagging temperature of the coal.

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Fig. 2(a) : Diagram of a generic moving bed gasifier

Fig. 2(b): Diagram of a generic fluidized bed gasifier

Fig. 2(c): Diagram of a generic entrained flow gasifier

Although large scale operation by entrained-bed type has successfully demonstrated and employed commercially, the experience is not long enough as fixed or fluidized-bed gasifiers. Also most prominent disadvantage of entrained-bed gasifier is in its high capital cost involved due to condensed configuration of parts. Fluidized-bed has been developed basically for the application to low-grade fuels or feedstock, like a lowgrade coal and wastes that contain various materials. Operating principle of fluidized bed involves even distribution of oxidizing agent through the distribution plate in bubbling type, or through the reactor in circulating type. Most prominent fluidized-bed examples are FBC boiler and waste pyrolysis plants. Fixed-bed has a long history of industrial experience as a so-called Lurgi type, which is still used in a large number in China. Due to its long industrial experience, it’s reliable. But it’s not suitable for the single large scale gasifier. Lurgi recently has achieved to make a gasifier of 1,600 ton/day capacity. Table 3. Comparison of typical three gasifier types

Entrained-bed

Fluidized-bed

Fixed-bed

Residence time in reactor

Item

3-5 sec

minutes

>30 min

Single unit size

Medium-Very large

Medium

Medium

Pressurized reactor

Easy

Not-easy

Not-easy

Complexity

Complex

Complex

Simple

Coal particle size

< 100 microns

6-10 mm

6-50 mm

Coal range

All ranks

Limit in agglomerating coals

Limit in agglomerating coals

Oxygen consumption (O2/coal ratio)

Large (0.9-1.0)

Medium

Low (0.7-0.8)

Tar formation

None or Very little

Small

Many

Industrial experience

From 1980’s

From 1970’s

From 1930’s

Advantages

Large scale operation

Suitable for low grade fuels Reliable

Disadvantages

Expensive

Difficult in scale-up, Not suitable for fines

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Limit in size




3.2 Commercially Available Large-Scale Gasifiers : Many organizations develop different types of gasifier commercially. Four gasification technologies have been proven at the large scale (>1250 tpd) needed for IGCC applications and some other are on developing stage. This section briefly discusses the 7 major gasifier concepts by providing a little the history of the development of each gasifier type and giving a general description as to the type of reactor each gasifier is, such as refractory lined, slurry fired, etc. 3.2.1 Lurgi Dry-Ash Gasifier: Lurgi gasifiers have gasified more coal than any other commercially available gasification process. Lurgi gasifiers use a moving bed design and operate below the ash melting point of the feed. The coal does not have to be finely milled, only crushed. In fact, one of the disadvantages of the Lurgi process is its inability to handle coal fines. The coal is fed into the top of the gasifier via lockhoppers. Oxygen is injected at the bottom of the gasifier and reacts with the coal which has been pre-heated by the hot syngas rising through the coal bed. Ash drops off the bottom of the bed and is depressurized via a lockhopper. The process was originally developed by Lurgi GmbH in the 1930s in Germany. In total more than 150 Lurgi gasifiers have been built with the largest being able to process 1000 tpd of coal on a moisture & ash-free basis. The two most prominent applications of the Lurgi process are not IGCCs: the coal-to-gasoline refineries of Sasol in the Republic of South Africa and the Dakota Gasification Synthetic Natural Gas plant in North Dakota. Both applications feature a series of oxygen-blown gasifiers and use low rank coal from nearby mines as the feedstock. A key disadvantage of the Lurgi process in IGCC applications is the production of hydrocarbon liquids in addition to syngas. The liquids represent about 10% of the heating value of the feed and therefore must be utilized in order to achieve competitive efficiencies. The other drawback of the Lurgi process is the need to stay below the ash melting point of the coal. For lower reactivity coals such as bituminous coal from the eastern US, this will result in lower carbon conversion due to the lower gasification temperatures. Conversely, low rank, high ash coals provide a competitive advantage for the Lurgi process versus its higher operating temperature competitors. 3.2.2 GE Energy The GE Energy gasification process has the most extensive track record in IGCC applications. Originally developed by Texaco in the 1950s, the technology was purchased by GE from Chevron-Texaco in 2004. The process uses an entrained flow, refractory-lined gasifier which can operate at pressures in excess of 62 bara (900 psia). The coal is fed to the gasifier as coal-water slurry and injected into the top of the gasifier vessel. Syngas and slag flow out the bottom of the gasifier. Three options are available for heat recovery from the GE Energy process: Quench, Radiant, and Radiant & Convective. In the Quench option, both the syngas and slag are forced into a water bath where the slag solidifies and the syngas is cooled and saturated with water vapor. The slag is removed from the bottom of the quench section via a lockhopper while the saturated syngas is directed to gas clean-up equipment. In the radiant option, the syngas and slag enter a long, wide vessel which is lined with boiler tubes. The vessel is designed to cool the syngas below the melting point of the slag. At the end of the radiant vessel both the syngas and slag are quenched with water. In the radiant plus convective option instead of having a water quench for both the syngas and slag, only the slag drops into a water bath at the bottom of the radiant vessel. The syngas exits at the side of the vessel and enters a convective syngas cooler. Both fire tube boiler and water tube boiler designs have been used for the convective cooler. More than 100 commercial applications of the GE Energy gasification process have been licensed since the 1950s. Some of the most notable examples are described below. It was used in the first US IGCC, the Cool Water project, which was built in the early 1980s by a consortium of power industry organizations including Southern California Edison and EPRI. It also received production subsidies from the federal synfuels program operated by the Treasury Department. The Cool Water IGCC operated for five years starting in 1984 and gasified a total of 1.1 million tons of bituminous coal while proving the IGCC concept. After the demonstration period, the gasification block was sold, dismantled and moved to Kansas where it became the heart of a

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petroleum coke-to-ammonia plant. The GE Energy process was also used at Tampa Electric Company’s Polk County IGCC. 3.2.3 Shell Gasifiers: The Royal Dutch Shell group of companies (Shell) has developed two different gasification processes. The first, called the Shell Gasification Process or SGP, was developed to gasify liquid and gaseous feedstocks. It features a refractory-lined gasifier with a single feed injection point at the top of the gasifier. The gasification products pass through a syngas cooler before entering a wet scrubber. The second process, called the Shell Coal Gasification Process (SCGP), was developed specifically to gasify solid feeds. The SCGP gasifier features a water-cooled “membrane wall” similar to the membrane walls used in conventional coal boilers. There are four feed injectors oriented horizontally in the mid-section of gasifier vessel. Slag flows out of a slag tap at the bottom of the vessel where it falls into a water bath and syngas flows out the top of the vessel. As the syngas exits the gasifier it is quenched with cool, recycled syngas to a temperature well below the ash melting point of the coal. The quenched syngas is still quite warm (typically 900°C) and passes through a syngas cooler and a dry solids filter before a portion of the gas is split off for recycle to the quench zone. The coal is fed to the SCGP gasifier pneumatically using high pressure nitrogen as the transport medium. The coal must first be dried and finely ground in a roller mill where warm, inert gas flows through the mill to remove the coal’s moisture. The dried coal is then pressurized via a system of lockhoppers. SCGP gasifiers operate at pressures up to approximately 40 bar. Shell began development of the SGP process in the 1950s, and work on the SCGP process started as a joint project with KruppKoppers in the mid-1970s. Both companies agreed to go their separate ways in the development of coal gasification in 1981, and KruppKoppers developed a competing dry-feed, membrane wall gasifier with the trade name PRENFLO. The only commercial application of the PRENFLO process has been the 280 MW Elcogas IGCC in Puertollano Spain. In 1999, Shell and Krupp Uhde agreed to join forces again in coal gasification. However, now only SCGP is being offered commercially by the two organizations. The first commercial application of SCGP was the 250 MW Demkolec IGCC built in 1994 in Buggenum, The Netherlands. The plant was originally owned by a consortium of Dutch electric utilities, but was sold to Nuon in the late 1990s. It is now operating as an independent power producer in the deregulated Dutch electricity market. Shell has also sold licenses for 12 SCGP gasifiers which will be used in coal-to-chemicals projects in China. The first of those projects is expected to begin operations in 2006. Perhaps the greatest advantage of Shell’s coal gasification process is its feed flexibility. The 240 tpd SCGP demonstration built at Shell’s refinery in Deer Park, Texas in the 1980s was able to process a full range of feedstocks including lignite, sub-bituminous coal, bituminous coal and pet coke. The biggest disadvantage of the SCGP has been its higher capital cost which is inherent in the more expensive nature of the gasifier design (boiler tubes are more expensive than refractory brick) and its dry feed system.

3.2.4 ConocoPhillips E-Gas ConocoPhillips owns the E-Gas gasification technology which was originally developed by Dow Chemical. The E-Gas process features a unique two-stage gasifier design. The gasifier is refractory-lined and uses coal-water slurry feed. The first stage of the gasifier has two opposed, horizontally-oriented feed injectors. The syngas exits the top of the first stage and slag flows out of the bottom into a water bath. The syngas produced by the first stage enters the second stage at temperatures comparable to the exit temperatures of theother two entrained flow gasifiers, GE Energy and SCGP. Additional coal-water slurry is injected into this hot syngas in the second gasifier stage, but no additional oxygen is injected. Endothermic gasification reactions occur between the hot syngas and the second stage coal feed. This lowers the temperature of the syngas and increases the cold gas efficiency of the process. Upon exiting the top of the second stage of the gasifer, the syngas passes through a syngas cooler which features a firetube design. The cooled syngas then enters a rigid barrier filter where any unconverted char from the second stage is collected and recycled back to the first stage of the gasifier where the hotter temperatures ensure near complete carbon conversion. Paper No : E-IIB-3




Dow began development of the E-Gas process in 1976 with a bench scale reactor. The work progressed to a 36 tpd pilot plant and then a 550 tpd “proto plant” located at Dow’s chemical manufacturing complex in Plaquemine, Louisiana. The main feedstock tested in these early gasifiers was lignite.

(a) Lurgi Dry-Ash Gasifier

(b) GE Energy Gasifier

(c) Shell Gasifier

(d) ConocoPhillips E-Gas Gasifier.

Figure-3 : Available commercial Gasifiers

3.2.5 KBR Transport Gasifier : Kellogg, Brown, & Root (KBR) Transport Gasifier (also known as TRIG™ Transport Integrated Gasification) is an advanced, circulating, fluidized-bed reactor. It was tested and proven at the Power Systems Development Facility (PSDF) in Wilsonville, Alabama. The facility was developed by KBR and Southern Company, together with the U.S. Department of Energy (DOE), and houses an engineering-scale demonstration unit of the gasifier. A series of tests beginning in 1999 have demonstrated stable, steady-state operation under a variety of conditions and feedstocks. The KBR Transport Gasifier is the basis for the integrated gasification combined cycle (IGCC) project in Kemper County, Mississippi, which will use air to gasify Mississippi Lignite coal, which is being mined close to the plant location. Figure 4(a) is a diagram of the KBR gasifier. Dried, pressurized, pulverized coal is fed into the mixing zone of the gasifier. The oxidant is added at the bottom of the mixing zone. The gasifier temperature is maintained below the ash melting point of the coal, and this favors the use of air rather than oxygen as the nitrogen in the air serves to moderate the temperatures within the fluidized bed, while also supplying the velocity needed to entrain the solids. Oxygen-blown operation has also been tested at the PSDF and would be the preferred mode for polygeneration applications in which chemical products were produced as well as power. Because of its lower operating temperature and its dry feed arrangement, the KBR reactor is most attractive for lower rank, high moisture coals. The lower temperatures also eliminate the need for refractory lining of the gasifier vessel. The PSDF Transport Gasifier can process 38 tpd of coal in air-blown mode. 3.2.6 British Gas/Lurgi Gasifier: The British Gas/Lurgi (BGL) coal gasifier is a dry-feed, pressurized, fixed-bed, slagging gasifier. The reactor vessel is water cooled and refractory lined. Each gasifier is provided with a motor-driven coal distributor/mixer to stir and evenly distribute the incoming coal mixture. Oxygen and steam are introduced into the gasifier vessel through sidewall-mounted tuyeres (lances) at the elevation where combustion and slag formation occur. The coal mixture (coarse coal, fines, briquettes, and flux) which is introduced at the top of the gasifier via a lock hopper system gradually descends through several process zones. Coal at the top of the bed is dried and devolatilized. The descending coal is transformed into char, and then passes into the gasification (reaction) zone. Below this zone, any remaining carbon is oxidized, and the ash content of the coal is liquified, forming slag. Slag is withdrawn from the slag pool by means of an opening in the hearth plate at the bottom of the gasifier vessel. The slag flows downward into a quench chamber and lock hopper in series. The pressure differential Paper No : E-IIB-3




between the quench chamber and gasifier regulates the flow of slag between the two vessels. Product gas exits the gasifier at approximately 1050°F (566°C) through an opening near the top of the gasifier vessel and passes into a water quench vessel and a boiler feed water (BFW) preheater designed to lower the temperature to approximately 300°F (150°C). 3.2.7 MHI Air-Blown Gasifier: MHI has developed a two-stage, air-blown gasifier which will be used in the 250 MW Clean Coal Power R&D Co. Ltd. IGCC being built near Iwaki City in Japan. Construction began in 2004, and the plant is scheduled to begin operation in 2007. The MHI gasifier operates in slagging conditions and, like the E-Gas process, injects coal without oxidant in the second stage. However, the gasifier features a water-cooled membrane wall rather than refractory lining and uses dry feed of coal rather than coalwater slurry. Unconverted char exiting the second stage is captured by a dry solids filter and returned to the fi rst stage where coal and air are injected, as figure 4(c). The MHI gasifier has also been tested in the 1990s at a 200 tpd demonstration unit located at the same site where the Clean Coal Power R&D IGCC plant is being built.

(a)KBR Transport Gasifier

(b) BGL Gasifier

(c) Simplified Drawing of the MHI Gasifier

Figure-4 : Available commercial Gasifiers

3.3 Performance comparison : Key factors in deciding the suitable gasifier type will be discussed in this section. As shown in Table 1, currently known coal gasifiers can be classified with choices on the reactor type which will decide the residence time in gasifier, coal feeding method and location, gasifier stages and number of burner nozzles to supply reactants, gasifier wall type in protecting the metal gasifier wall, whether coal ash will be converted to slag or just fly-ash, and the oxidant whether to use oxygen or air. Table 1. Currently available commercial coal gasifiers Item Country

ConocoPhillips Netherlands Germany USA Shell

Uhde

Reactor Type

Entrained

Entrained Entrained

Feeding

Dry/Side

Dry/Side

Stages

1

1

Wall

Slurry/ Side 2

Siemens Germany

GE Energy USA

Entrained Entrained Dry/Top 1

Slurry/ Top 1

MHI

OMB

Lurgi

Japan

China

Germany

Entrained Entrained Dry/Side

Dry/Side

2

1

Membrane Membran Refractory Membran Refractory Membran Membrane e e e

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Fixed Dry/ Top 1 -




Slagging

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Oxidant

O2

O2

O2

O2

O2

Air

O2

Burners

4

4

2+1

1

1

4+4

4

No Air/O2 -

First of all, most important remark will be that there is no universal coal gasifier to meet all the different technical requirements. Each gasifier has developed to meet the specific needs from the customers and should see where the preferred gasifier type has the most proven experience in the industry. One of the most frequently asked question is that a specific gasifier can be utilized interchangeably both for the power generation and for the chemical production. If the plant size is small, this option might be possible with limited option. But most commercial gasification plants usually cost 10-200 million US$. With this high capital cost, the gasifier which is the core part of the plant should be designed to maximize the wanted final product with highest efficiency, along with minimum maintenance and without any accident. Manufacturing limit in the coal gasifier should be evaluated in terms of pressure, gasifier diameter, and manufacturing equipments. Coal gasifier is basically a pressure vessel which has a practical manufacturing limit simply by available steel rolling machine and by economics of manufacturing cost. Manufacturing a pressure vessel above 100 bar would not be practical purely due to the manufacturing ability of 3,000 ton/day scale gasifier as a single vessel, and it is never be economical since the wall thickness of large coal gasifier might be too large. Pilot scale coal gasifiers are treating the coal in 1-30 ton/day range, in that no practical problem exists in manufacturing unless the size is too compact so that space for nozzles and cooling pipes is simply not available.

4. COAL GASIFICATION PROSPECT IN BANGLADESH Energy crisis is becoming the first national problem of Bangladesh. Coal Gasification could be the solution to overcome these challenges. And Integrated Gasification Combined Cycle power (IGCC) plant could be a possible solution to meet the ever increasing demand for power. It could replace many of the contractual highcost rental power plants and small Industrial Power Plants in Bangladesh. Bangladesh is very lucky that it has got substantial natural gas reserve and significant but almost untapped high quality coal resource. There is also plenty of scope to generate solar power, wind power and energy from bio fuels. Many countries of the world like Japan, Korea do not have any fossil fuel resource yet they are among the top developed nations. They import almost their entire requirement of the fuel for energy generation from highly competitive energy market. Several countries do not have enough basic fuel to meet their huge demand. These countries import energy from energy rich countries to fuel their economy. Unfortunately, our small country Bangladesh of 160 million people has no appropriate strategy. There is an energy policy, which is not properly administered. Till date five major coalfields have been discovered in Bangladesh. In order of discovery year these are Jamalganj (1962), Barapukuria (1985), Khalashpir (1989), Dighipara(1995) and Phulbari (1998). At present coal is being produced commercially only from the Barapukuria underground coal mine in Dinajpur district that has gone through a period of 8 years of construction and one year of production. Current production rate is about 1500 tons per day. The plan to establish an open-pit mine in nearby Phulbari was aborted last year in the wake of mass protest by the local people. Coal in the Jamalganj-Paharpur area is too deep to mine. Most of the energy experts believe that there is no option for Bangladesh other than mining its coal for power generation, because the future power demand cannot be meet from gas-based power plants, as the gas reserve is too limited to run for long. At present, the only coal-based power plant (250MW) in the country is in operation near Barapukuria coalmine, which feeds the plant.

TABLE 1. MAJOR COAL FIELDS AND PROVED COAL RESERVES IN BANGLADESH Coal field (district) Jamalganj (Joypurhat) Barapukuria (Dinajpur) Khalashpir (Rangpur) Paper No : E-IIB-3

Depths of Reserve Year of Discover No. of coal seam (million discovery ed by coal seam (meter) ton) 1962

SVOC

640-1158

7

1053

1985

GSB

118-506

6

303

1989

GSB

257-451

8

147

Status Mining not feasible economically Underground mine started production Undeveloped




Dighipara (Dinajpur) Phulbari (Dinajpur)

1995

GSB

250

7

200

Undeveloped

Open pit mine feasibility study undertaken in 2004 **Source Petrobangla; Geological Survey of Bangladesh

1997

BHP

152-246

1

380

4.1 Base Electricity Power Plant In 2012, Bangladesh’s primary energy consumption was an estimated 56% natural gas, 24% traditional biomass and waste, 16% oil, 3% coal, and 1% hydropower and solar []. According to power sector master plan, the target of electricity generation by the year 2021 is 24,000 megawatt and 39,000 megawatt by the year 2030. The government planned to lower the use of gas in electricity generation to 25 percent by 2030[34]. Also, it planned to generate 50 percent electricity from coal. An integrated gasification combined cycle (IGCC) is a technology that uses a gasifier to turn coal into synthesis gas (syngas) [45-46]. It then removes impurities from the syngas before it is combusted. Some of these pollutants, such as sulfur, can be turned into re-usable by-products. This results in lower emissions of sulfur dioxide, particulates, and mercury. Excess heat from the primary combustion and syngas fired generation is then passed to a steam cycle, similar to a combined cycle gas turbine. These results in improved efficiency compared to conventional pulverized coal. As far as IGCC power generation is concerned, there are six coal based units in the world, 253MW-BuggenumNetherland, 262MW-Indiana-USA, 250MW-Florida-USA, 300MW-CiudadReal-Spain, 430MW-CzechRepublic and 250MW- Fukushima-Japan[7]. However, a small number of new projects have been initiated worldwide, each at some stage of planning or construction. According to National Energy Technology Laboratory, already 35 projects have proposed in worldwide to generate 20,730MW electricity by IGCC plant where the US proposed the maximum individual IGCC plant (11,775MW by 20 projects), followed by UK (2,540MW by 4 projects), Saudi Arabia (2,400MW by 1 project) and China (1,0505MW by 2 projects) [7]. Bangladesh government should take lesson from the worldwide scenario of electricity generation from coal. To decrease the dependency on gas and produce clean electricity, this is the perfect time to employing IGCC technology in Bangladesh. 4.2 Substitution of Natural Gas Bangladesh, the seventh largest natural gas producer in Asia in 2012, produced 772 billion cubic feet, all of which was domestically consumed. Natural gas production in Bangladesh has increased by an annual average of 7% over the past decade, from 2002 to 2012. However, Bangladesh is facing acute natural gas supply shortages especially in the electricity sector. These shortages, in turn, have led to rolling blackouts of electricity. Platts estimates that Bangladesh must increase its natural gas supply by at least 18% to eliminate natural gas supply shortages. Because the increasing demand for natural gas (methane) in the Bangladesh and the limited domestic supply, foreign natural gas imports have grown and the cost has risen very quickly. There are at least 5 process methods for conversion of coal to SNG as named 1.Steam-Oxygen Gasification, 2. Catalytic Steam Gasification, 3.Hydrogasification, 4.Underground Steam-Oxygen Gasification, 5.Underground Hydrogasification. 4.3 Cement Industry Coal is used as an energy source in cement production. Large amounts of energy are required to produce cement. It takes about 200 kg of coal to produce one tonne of cement and about 300-400 kg of cement is needed to produce one cubic meter of concrete. Over 3.3 billion tonnes of cement were consumed globally in 2010. Bangladesh has bright future in cement production. Here coal gasification process can be used in the kiln and the ash from gasifier as fly ash. 4.4 Brick Fields Bangladesh has about 6,000 authorized brickfields and numerous illegal ones. The brickfield are typically small independent units and operate 24 hours during the dry season. They are located near towns or major construction sites. In Dhaka, there are around 4,500 brick kilns in operation producing 9.0 billion bricks per year. The largest brick making zone is on the north of Dhaka city, where more than 1000 brick field are situated. The existing technology for firing kiln are fixed chimney kiln(FCK) and bull’s trench kiln (BTK) through last one is banned in Bangladesh contributes 16% of production. The main raw materials used in brick kilns to dry bricks are firewood and coal. The department of environment said that the 4,000 brick kilns burn nearly 20 lakh

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tons of coal and another 20 lakh tons of wood every year to meet the demand for 400 to 1200 tons of fuel. In this scenario, coal gasification technology can be employed to burn brick without polluting environment.

5. PROPOSED COAL-GASIFICATION BASED SYNGAS ENERGY INFRASTRUCTURE In this paper, we proposed an infrastructure, which based on Coal-Syngas. In this infrastructure coal is converted to syngas by a central gasification plant, which will situated at high density industrial area. Then, the produced syngas purified through purification plant situated beside of gasification plant. Then cleaned syngas processed to make Synthesis Natural Gas (SNG) in syngas transmission station. The syngas transmission station will maintain a fixed pressure in pipeline transmission, for this purpose there would be a large reserver to reserve syngas in the time of peak generation. Then it transmitted through a dedicated pipeline or injected into existing natural gas pipeline. The syngas distributed station will manage the distribution among the different types of user like Household, Thermal Power Plant, Brick Field, Ceramics & Glass Industry and any kind of thermal process industry. This proposed technology will reduce the dependency on natural gas and help to build a sustainable energy plan for future. Energy crisis is becoming the first national problem of Bangladesh. The proposed infrastructure could finance by government or the International Organization who donates for health or environmental issues, like World Health Organization (WHO). Coal syngas can be transmitted through pipeline.

Coal

Gasifier Plant

Purification Plant

Syngas Transmission Station

Pipe line Transmission

Syngas Distribution System

In Plant Electricity Generation

Air/O2 Steam

ASH: Used in Brick Field Cement Factory

Tar oil: Used in Bitumen Production

CO2 (Used in oil refinery, underground storage) H2 (Electricity generation by fuel cell) Methane (Used in chemical industries) Sulphur (Raw gas for producing sulphuric acid) CO (Used in process chemical) **And many industrial purpose

Electricity Generation Brick Field Steel Industry

Pipe line Distribution

Cleaned Syngas

Ceramic & Glass Industry Substitution of Natural Gas Any Kind of Thermal Process

Fig. 3 Proposed Coal Gasification Based Energy Infrastructure. Similarly, the syngas production cost decreases with increasing coal quality and ranges from $15.6/GJ to $19.3/GJ. The production cost is dominated by the investment cost. However, costs may significantly depend on location. Chinese plants may cost 60%-65% of the US and European installations. Syngas may be further upgraded to meet specific demands. Co-production of a 20% of H2 using a H2 separation unit is only slightly more costly than the basic process, resulting in 5% higher capital and 4% higher product costs. The conversion into synthetic natural gas (SNG), i.e. pipeline quality gas, requires additional processes and costs. If the syngas is converted into SNG, the capital cost increases by approximately 25% and the cost of the final product increases by 40%, while the conversion efficiency of the process decreases by some 14 percentage points, reaching about 60%. Considering the competitive market, it would be convenient for BPDB to make necessary arrangement for coal sourcing (e.g. offtake agreement with producers) from these countries under the active support of the government. According to The Center for Environmental and Geographic Information Services (CEGIS) recommendation, the following suggestions may be made: >> Coal should be procured from multiple sources (multiple suppliers and multiple countries) for ensuring continuous and sustainable supply. >> Australia would be a sustainable source for coal of higher GCV value (above 6000 kcal/kg). Indonesia would be suitable source for coal of 5000 to 5800 GCV subject to above mentioned challenges are successfully handled

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>> Long term agreement with coal trader/suppliers would be suitable mode of coal sourcing (considering present knowledge of mine operation and investment) >> Long term agreement needs to be made with multiple coal transportation agents/shippers for continuous supply of coal. >> BPDB will need to engage a survey and inspection agent for proper inspection and monitoring of coal supply system, coal quality and coal quantity. >> Govt. should form a dedicated team comprising Ministry, BPDB, and other stakeholders at the earliest possible time with the responsibility of initiating coal sourcing and transportation. >> Government should also assign responsible officers in the Embassy of Bangladesh at Jakarta, Indonesia and High Commission of Bangladesh at Canberra, Sydney and South Africa for coordinating the coal supply to Bangladesh. There are enough coal resources in reachable distance to Bangladesh. Price per kcal, reliability of the source and the convenience of the transportation chain will be the criteria influencing the decision making process. BPDB should thoroughly define their advantages in this process. The long-term demand and the support of the Government are major assist in these negotiations. Generally, the mining companies prefer this long-term thinking as well, traders like the “quick money”. The development of the domestic resources should become a part of this strategy. It well might be that the mining companies providing the import coal are of assistance to develop the domestic resources.

6. CONCLUSIONS Growing emphasis on coal gasification technology is aimed at reducing the environmental impact of coal energy conversion. Four gasification technologies have been developed and demonstrated at sizes compatible

with large scale IGCCs. Three of these technologies are based on entrained flow reactors which rapidly convert coal to a hot syngas. The fourth is based on a moving bed reactor which uses long residence times to convert the coal and produces a more moderate temperature syngas along with liquid hydrocarbons. Several other gasification technologies are nearing demonstrations of large scale gasifier which could be used in IGCCs. The most appropriate gasifier to use in an IGCC is probably more a function of the type of coal to be gasified than anything else. Lower rank, high moisture coals are more capable with dry-fed gasifiers, while high temperature slagging gasifiers are best for high rank coals which are less reactive. The performance of existing commercial gasifier are investigated including their brief history. The possible application and prospects of coal gasification in Bangladesh are discussed here. A coal gasification based infrastructure for Bangladesh is discussed also. Bangladesh Government is committed to clean energy and going to use large amount of coal for electricity production, therefore, government should ensure energy security for future by establishing coal based IGCC power plant as earliest as possible.

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AUTHORS Md. Kamruzzaman received his B.Sc. Engg. degree in Electrical and Electronic Engineering from Ahsanullah University of Science and Technology(AUST), in 2009. At present, he is continuing postgraduate study, under the department of Electrical & Electronic Engineering in Dhaka University of Engineering and Technology(DUET), Bangladesh. He is now serving as Sr. Lecturer in Electrical and Electronic Engineering department at Atish Dipankar University of Science and Technology, Dhaka, Bangladesh. His research interests include Energy, Coal Gasification, RF Engineering, Power System and Renewable Energy. Kamruzzaman is a member of The Institution of Engineers, Bangladesh (IEB).

Md. Raju Ahmed received B.Sc. from Chittagong University of Engineering and Technology, Bangladesh, M.Sc. from Bangladesh University of Engineering and Technology, Bangladesh, and Dr. of Engg. Degree from the University of Tokyo, Japan in 2003, 2006 and 2013 respectively, all in Electrical and Electronic Engineering. He joined Dhaka University of Engineering and Technology(DUET), Bangladesh in 2004, and has been an associate professor since 2013. He has published a good number of research papers in international conferences and journals. Dr. Ahmed is a member of Institution of Engineers of Bangladesh (IEB).

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