Takeharu Hasegawa

A Study of Combustion Characteristics of Gasified Coal Fuel

The development of integrated, coal-gasification combined cycle (IGCC) systems provides cost-effective and environmentally sound options for meeting future coal-utilizing power generation needs in the world. The Japanese government and the Electric Power Industries in Japan promoted research and development of an IGCC system. We have being working on developing a low-NO x combustion technology used in gas turbine combustors for IGCC. Each gaseous fuel produced from some raw materials contained CO and H 2 as the main combustible components, and a small amount of CH 4 . Compositions and calorific values of gasified coal fuels varied widely depending on raw materials and gasifier types. Gaseous fuel, produced in various gasifiers, has a calorific value of 4-13 MJ/m 3 . which is about one-tenth to one-third that of natural gas. The flame temperatures of fuels increase as the fuel calorific value rises. When the fuel calorific value rises 8 MJ/m 3 or higher, the flame temperature is higher than that of natural gas, and so NO x production from nitrogen fixation is expected to increase significantly. Also, some gasified coal fuels contain fuel nitrogen, such as ammonia, if the hot/dry type gas cleaning system is employed. These factors affect the combustion characteristics of the gasified coal fuel. In this paper, we clarified the influence of gasified coal fuel properties on NO x and CO emissions through experiments using a small diffusion burner and through numerical analysis based on reaction kinetics. The main results were as follows: 1 NH 3 conversion to NO x increases with increasing CH 4 concentration in gaseous fuel. 2 If gaseous fuel contains CH 4 , there will be some specific equivalence ratio in the primary combustion zone for the minimum NH 3 conversion to NO x in the two-staged combustion. 3 Its specific equivalence ratio in the primary combustion zone increases with decreasing CH 4 concentration in gaseous fuel. 4 If the fuel contains a small percent of CH 4 , there is no influence of the CO/H 2 molar ratio in the fuel on the conversion rate of NH 3 to NO x , while there is an influence in the case where fuel contains no CH 4 . The conversion rate increases with rises in the CO/H 2 molar ratio. 5 As the pressure increases, the conversion rate of NH 3 to NO x slightly decreases and the CO emission declines significantly.

Effect of Pressure on Emission Characteristics in LBG-Fueled 1500°C-Class Gas Turbine

Developing integrated coal gasification combined cycle (IGCC) systems ensures cost-effective and environmentally sound options for supplying future power generation needs. In order to enhance thermal efficiency of IGCC and to reduce NO x emission, a 1500°C-class gas turbine combustor for IGCC was designed, tested, and the performance of the combustor was evaluated under pressurized conditions. The designed combustor had the following three characteristics: (1) in order to assure the stable combustion burning low-Btu gas (LBG), an auxiliary combustion chamber was installed at the entrance of the combustor; (2) to reduce fuel NO x emission that was produced from the ammonia (NH3) in the fuel, the rich-lean combustion method was introduced; and (3) to compensate for the declined cooling-air associated with the higher temperature of the gas turbine, the tested combustor was equipped with a dual-structure transition piece so that the cooling air in the transition piece can be recycled to cool down the combustor liner wall. As a result of combustor tests, it is confirmed that CO emission is less than 20 ppm, the conversion rate of NH3 which contains about 1000 ppm in the coal gasified fuel to NO x shows 40 percent or below, and the liner wall temperature remained below almost 850°C under high pressure (1.4 MPa), rated load condition.

Development of Low NOx Combustion Technology in Medium-Btu Fueled 1300°C-Class Gas Turbine Combustor in an Integrated Coal Gasification Combined Cycle

The development of integrated coal gasification combined cycle (IGCC) systems ensures higher thermal efficiency and environmentally sound options for supplying future coal utilizing power generation needs. The Japanese government and electric power industries in Japan promoted research and development of an IGCC system using an air-blown entrained-flow coal gasifier. On the other hand, Europe and the United States are now developing the oxygen-blown IGCC demonstration plants. Gasified coal fuel produced in an oxygen-blown entrained-flow coal gasifier has a calorific value of 8-13 MJ/m 3 which is only 1/5-1/2 that of natural gas. However, the flame temperature of medium-Btu gasified coal fuel is higher than that of natural gas and so NO x production from nitrogen fixation is expected to increase significantly. In the oxygen-blown IGCC, a surplus nitrogen produced in the air-separation unit (ASU) is premixed with gasified coal fuel (medium-Btu fuel) and injected into the combustor, to reduce thermal-NO x production and to recover the power used for the ASU. In this case, the power to compress nitrogen increases. Low NO x emission technology which is capable of decreasing the power to compress nitrogen is a significant advance in gas turbine development with an oxygen-blown IGCC system. Analyses confirmed that the thermal efficiency of the plant improved by approximately 0.3% (absolute) by means of nitrogen direct injection into the combustor, compared with a case where nitrogen is premixed with gasified coal fuel before injection into the combustor. In this study, based on the fundamental test results using a small diffusion burner and a model combustor, we designed the combustor in which the nitrogen injection nozzles arranged on the burner were combined with the lean combustion technique for low-NO x emission. In this way, we could reduce the high-temperature region, where originated the thermal-NO x production, near the burner positively. And then, a combustor with a swirling nitrogen injection function used for a gas turbine, was designed and constructed, and its performance was evaluated under pressurized conditions of actual operations using a simulated gasified coal fuel. From the combustion test results, the thermal-NO x emission decreased under 11 ppm (corrected at 16% O 2 ), combustion efficiency was higher than 99.9% at any gas turbine load. Moreover, there was different effects of pressure on thermal-NO x . emission in medium-Btu fuel fired combustor from the case of a natural gas fired combustor.

Reaction of Fuel NOx Formation for Gas Turbine Conditions

Ammonia contained in coal-gasified fuel is converted to nitrogen oxides (NO{sub x}) in the combustion process of a gas turbine in integrated coal gasification combined cycle (IGCC) system. Research data on fuel-NO{sub x} formation are insufficient, and there still remains a wide explored domain. The present research aims at obtaining fundamental knowledge of fuel-NO{sub x} formation characteristics by applying reaction kinetics to gas turbine conditions. An instantaneous mixing condition was assumed in the cross section of a gas turbine combustor and both gradual mixing condition and instantaneous mixing condition were assumed at secondary air inlet section. The results may be summarized as follows: (1) in the primary combustion zone under fuel rich condition, HCN and other intermediate products are formed as ammonia contained in the fuel decomposes; (2) formation characteristics of fuel-NO{sub x} are affected by the condition of secondary air mixing; and (3) the conversion ratio from ammonia to NO{sub x} declines as the pressure inside the combustor rises under the condition of gradual mixing at the secondary air inlet. These results obtained agreed approximately with the experimentation.

A Study of Low NOx Combustion in Medium-Btu Fueled 1300 °C-Class Gas Turbine Combustor in IGCC

The development of integrated coal gasification combined cycle (IGCC) systems ensures cost-effective and environmentally sound options for supplying future coal utilizing power generation needs. The Japanese government and the electric power industries in Japan promoted research and development of an IGCC system using an air-blown entrained-flow coal gasifier. We worked on developing a low-Btu fueled gas turbine combustor to improve the thermal efficiency of the IGCC by raising the inlet-gas temperature of gas turbine.On the other hand, Europe and the United States are now developing the oxygen-blown IGCC demonstration plants. Coal gasified fuel produced in an oxygen-blown entrained-flow coal gasifier, has a calorific value of 8.6MJ/m 3 which is one fifth that of natural gas. However, the adiabatic flame temperature of oxygen-blown medium-Btu coal gaseous fuel is higher than that of natural gas and so NOx production from nitrogen fixation is expected to increase significantly. In the oxygen-blown IGCC system, a surplus nitrogen in quantity is produced in the oxygen-production unit. When nitrogen premixed with coal gasified fuel is injected into the combustor, the power to compress nitrogen increases. A low NOx combustion technology which is capable of decreasing the power to compress nitrogen is a significant advance in gas turbine development with an oxygen-blown IGCC system. We have started to develop a low NOx combustion technology using medium-Btu coal gasified fuel produced in the oxygen-blown IGCC process.In this paper, the effect of nitrogen injected directly into the combustor on the thermal efficiency of the plant is discussed. A 1300 °C-class gas turbine combustor with a swirling nitrogen injection function designed with a stable and low NOx combustion technology was constructed and the performance of this combustor was evaluated under atmospheric pressure conditions. Analyses confirmed that the thermal efficiency of the plant improved by 0.2 percent (absolute), compared with a case where nitrogen is premixed with coal gasified fuel before injection into the combustor. Moreover, this new technique which injects nitrogen directly into the high temperature region in the combustor results in a significant reduction in NOx production from nitrogen fixation. We estimate that CO emission concentration decreases to a significant level under high pressure conditions, while CO emission concentration in contrast to NOx emission rises sharply with increases in quantity of nitrogen injected into the combustor.Copyright

Study of Medium-Btu Fueled Gas Turbine Combustion Technology for Reducing Both Fuel-NOx and Thermal-NOx Emissions in Oxygen-Blown IGCC

In order to improve the thermal efficiency of the oxygen-blown IGCC (Integrated Gasification Combined Cycle) for stricter environmental standards and cost-effective option, it is necessary to adopt the hot/dry gas cleaning system. In this system, the flame temperature of medium-btu gasified fuel is higher and so NOx production from nitrogen fixation is expected to increase significantly. Also the gasified fuel contains fuel nitrogen, such as ammonia, in the case of employing the hot/dry gas cleaning system. This ammonia is easily oxidized into fuel-NOx in the combustor. For contribution to the protection of the environment and low cost operations of all kinds of oxygen-blown IGCC, low NOx combustion technology for reducing both the fuel-NOx and thermal-NOx emission has to be developed. In this paper, we clarified effectiveness of applying both the two-stage combustion and the nitrogen injection, and the useful engineering guidelines for the low-NOx combustor design of oxygen-blown gasified, medium-btu fuels. Main results obtained are as follows: (1) Based on the fundamental combustion tests using the small diffusion burner, we clarified that equivalence ratio at the primary combustion zone has to be adjusted due to the fuel conditions, such as methane concentration, CO/H2 molar ratio, and calorific values of gasified fuels in the case of the two-stage combustion method for reducing fuel-NOx emission. (2) From the combustion tests of the medium-btu fueled combustor the two-stage combustion with nitrogen direct injection into the combustor results in reduction of NOx emission to 80ppm (corrected at 16% O2) or less, the conversion rate of ammonia to NOx was 35% under the gas turbine operational conditions for IGCC in the case where fuel contains 3% of methane and 2135ppm of ammonia. By means of nitrogen direct injection, the thermal efficiency of the plant improved by approximately 0.3 percent (absolute), compared with a case where nitrogen is premixed with gasified fuel. The CO emission concentration decreased drastically, as low as 20ppm, or combustion efficiency was kept higher than 99.9%. Furthermore, based on the fundamental combustion tests’ results, the ammonia conversion rate is expected to decrease to 16% and NOx emission to 26ppm in the case of gasified fuel that contains 0.1% methane and 500ppm of ammonia. From the above results, it is clarified that two-stage combustion method with nitrogen injection is very effective for reducing both the fuel-NOx and thermal-NOx emissions at once in IGCC and it shows the bright prospects for low NOx and stable combustion technology of the medium-btu fuel.© 2002 ASME

Development of Low NOx Combustion Technology in Medium-Btu Fueled 1300 °C-Class Gas Turbine Combustor in IGCC

The development of integrated coal gasification combined cycle (IGCC) systems ensures higher thermal efficiency and environmentally sound options for supplying future coal utilizing power generation needs. The Japanese government and electric power industries in Japan promoted research and development of an IGCC system using an air-blown entrained-flow coal gasifier. On the other hand, Europe and the United States are now developing the oxygen-blown IGCC demonstration plants.Gasified coal fuel produced in an oxygen-blown entrained-flow coal gasifier, has a calorific value of 8–13MJ/m3 which is only 1/5–1/3 that of natural gas. However, the flame temperature of medium-Btu gasified coal fuel is higher than that of natural gas and so NOx production from nitrogen fixation is expected to increase significantly. In the oxygen-blown IGCC, a surplus nitrogen produced in the air-separation unit (ASU) is premixed with gasified coal fuel (medium-Btu fuel) and injected into the combustor, to reduce thermal-NOx production and to recover the power used for the ASU. In this case, the power to compress nitrogen increases. Low NOx emission technology which is capable of decreasing the power to compress nitrogen is a significant advance in gas turbine development with an oxygen-blown IGCC system. Analyses confirmed that the thermal efficiency of the plant improved by approximately 0.3 percent (absolute) by means of nitrogen direct injection into the combustor, compared with a case where nitrogen is premixed with gasified coal fuel before injection into the combustor.In this study, based on the fundamental test results using a small diffusion burner and a model combustor, we designed the combustor in which the nitrogen injection nozzles arranged on the burner were combined with the lean combustion technique for low-NOx emission. In this way, we could reduce the high temperature region, where originated the thermal-NOx production, near the burner positively. And then, a combustor with a swirling nitrogen injection function used for a gas turbine, was designed and constructed, and its performance was evaluated under pressurized conditions of actual operations using a simulated gasified coal fuel. From the combustion test results, the thermal-NOx emission decreased under 11ppm (corrected at 16% O2), combustion efficiency was higher than 99.9% at any gas turbine load. Moreover, there was different effects of pressure on thermal-NOx emission in medium-Btu fuel fired combustor from the case of natural gas fired combustor.Copyright

Effect of Pressure on Emission Characteristics in LBG-Fueled 1500 °C -Class Gas Turbine

Developing integrated coal gasification combined cycle (IGCC) systems ensures cost-effective and environmentally sound options for supplying future power generation needs. In order to enhance thermal efficiency of IGCC and to reduce NOx emission, a 1500 °C -class gas turbine combustor for IGCC was designed, tested and the performance of the combustor was evaluated under pressurized conditions. The designed combustor had three characteristics: 1) In order to assure the stable combustion burning low-Btu gas (LBG), an auxiliary combustion chamber was installed at the entrance of the combustor. 2) To reduce fuel NOx emission that was produced from the ammonia (NH3) in the fuel, the rich-lean combustion method was introduced. 3) To compensate for the declined cooling-air associated with the higher temperature of the gas turbine, the tested combustor was equipped with a dual-structure transition piece so that the cooling air in the transition piece can be recycled to cool down the combustor liner wall. As a result of combustor tests, it is confirmed that CO emission is less than 20ppm, the conversion rate of NH3 which contains about 1000ppm in the coal gasified fuel to NOx shows 40 percent or below, and the liner wall temperature remained below almost 850 °C under high pressure (1.4MPa), rated load condition.Copyright

A Study on Low NOx Combustion in LBG-Fueled 1500°C-Class Gas Turbine

Developing integrated coal gasification combined cycle systems ensures cost-effective and environmentally sound options for supplying future power generation needs. The reduction of NOx emissions and increasing the inlet temperature of gas turbines are the most significant issues in gas turbine development in an Integrated Coal Gasification Combined Cycle (IGCC) power generation systems. The coal gasified fuel, which is produced in a coal gasifier of air-blown entrained-flow type has calorific value as low as 1/10 of natural gas. Furthermore the fuel gas contains ammonia when a gas cleaning system is a hot type, and ammonia will be converted to nitrogen oxides in the combustion process of a gas turbine.This study is performed in a 1500°C-class gas turbine combustor firing low-Btu coal-gasified fuel in IGCC systems. An advanced rich-lean combustor of 150-MW class gas turbine was designed to hold stable combustion burning low-Btu gas and to reduce fuel NOx emission that is produced from the ammonia in the fuel. The main fuel and the combustion air is supplied into fuel-rich combustion chamber with strong swirl flow and make fuel-rich flame to decompose ammonia into intermediate reactants such as NHi and HCN. The secondary air is mixed with primary combustion gas dilatorily to suppress the oxidization of ammonia reactants in fuel-lean combustion chamber and to promote a reducing process to nitrogen.By testing it under atmospheric pressure conditions, the authors have obtained a very significant result through investigating the effect of combustor exit gas temperature on combustion characteristics. Since we have ascertained the excellent performance of the tested combustor through our extensive investigation, we wish to report on the results.Copyright

Study of NH3 removal from coal gasified fuel

Publisher Summary This chapter examines the effects of additive nitrous oxide (NO) and oxygen (O 2 ) concentration and the effects of carbon monoxide (CO) and hydrogen (H 2 ) in the coal-gasified fuel on the decomposition characteristics of ammonia (NH 3 ) and NO using the tubular flow reactor and by numerical analysis based on reaction kinetics. The optimum concentration of additive NO exists, by which remaining thin-film nanocomposite (TFN) after reacting under the reaction temperature of 1,000 °C is made minimum. When O 2 is added by 5,000 ppm with this coal-gasified fuel that contains NH 3 by 1,000 ppm, this optimum additive NO concentration is 1,000 ppm. This technique decreases the TFN by about 40% by adding 5,000 ppm of O 2 and1,000 ppm of NO to the coal-gasified fuel that contains NH 3 by 1,000ppm under the reaction temperature of 1,000 °C. The decomposition ratios of NH 3 and NO decrease as the H 2 concentration increases.