What are the characteristics of pressurized gasification technology?

The advantages of pressurized gasification are 1, high gasification capacity, 2, relatively smaller equipment, 3, reduced power consumption for compressing gas

I copied a long passage from the Internet: 1 Texaco gasification process 1.1 Structural features of the Texaco gasification process (1) Pulp preparation system. Coal and water are combined in conventional slurry mills to produce a coal water slurry with a concentration of typically 60%–68%; the designed concentration of the coal water slurry at the Tampa IGCC power plant is 68%. For some coals with a high ash fusion point or those that are difficult to pulped, limestone fluxes or coal slurry additives are often added to the coal slurry grinder to lower the ash fusion point of the coal or to improve the uniformity of the coal slurry. At the outlet of the slurry mill, there is a cylindrical sieve; the qualified slurry flows into the slurry storage tank, while the unqualified slurry overflows into the circulation tank and is sent back to the inlet of the slurry mill. A mixer is installed in the coal slurry tank, and an appropriate amount of water is added based on the measurement results, so as to keep the coal slurry in the tank in a uniform state at a constant concentration. The amount of slurry required by the gasification furnace is generally drawn from the slurry storage tank by a two-stage diaphragm pump and pressurized before being sent to the nozzle of the gasification furnace. Two-stage flow detectors are installed on the slurry delivery pipeline at the entrance of the gasification furnace to strictly control the flow rate of the slurry; the regulation of this flow rate is carried out entirely by the diaphragm pump. 　　(2) Gasifier and gas cooling system. Water-coal slurry and oxygen with 95% purity are simultaneously fed into the nozzle of the gasifier, where a gasification reaction takes place. The temperature in the reaction zone is generally between 1,200 and 1,500 °C, while the pressure in the gasifier can range from 2.5 to 8.5 MPa, depending on the requirements of different industries. The pressure in the gasifier of the Tampa IGCC power plant is 2.8–3.0 MPa, and the temperature in the gasification zone is 1,482 °C. Water, coal, and oxygen undergo gasification reactions in the gasifier, primarily producing CO, H2, CO2, H2O, CH4, H2S, and N2; in addition, small amounts of NH3, COS, HCN, and fly ash are also generated. Due to the use of water-coal slurry as the feed, the H2O content in the gas is relatively high. 　　The Texaco gasifier at the Tampa power plant is equipped with refractory bricks (usually 4 layers), with an inner diameter of about 4.0 m and a height of about 3.0 m. The gasification reaction occurs very rapidly, with the residence time of raw gas in the gasifier being generally 2–3 seconds. The hot gas leaves the gasifier and enters a specially designed radial cooler, where its temperature is reduced to 700 °C, simultaneously causing the molten slag contained in the hot gas to solidify. The cooled raw gas enters a convective cooler where it is further cooled to 480 ℃. The sensible heat in the gas is recovered in the secondary cooler, generating high-pressure saturated steam at 10.4 MPa. The gasifier is integrated with the radial cooler; it has an outer diameter of about 5 m, a height of about 39 m, and a total weight of around 900 t. The installation elevation of the gasifier is approximately 106.75 m. 　　(3) Slag and blackwater treatment system. The slag inside the gasifier is cooled by a radial cooler, where it solidifies into a glass-like form before entering a hopper system filled with water. There are two valves at each end of the hopper to control the inflow and outflow of slag. The slag discharged from the pressure lockhopper falls into the coarse slag bin, where the coarse slag is separated for further processing or sold directly. The fine sludge is pumped together with water into a fine ash sedimentation tank where gravity sedimentation or filtration takes place to separate the water from the fine sludge. The water containing ash that comes out of the washer also enters the sedimentation tank, where the carbon-containing fly ash is separated from the water. The water that overflows from the sedimentation tank generally contains only a very small amount of fine ash; this water is recycled to the inlet of the water washer as washing water, while any excess water is sent back to the coal slurry preparation system. The fine ash that flows out from the bottom of the sedimentation tank enters a filter press, where it is turned into fine ash cakes. The Tampa power plant employs a process of recycling fine ash back to the coal slurry mill, with the aim of improving carbon conversion rates. 1.2 Analysis of the Performance and Operational Parameters of the Texaco Gasification Process Performance characteristics of the Texaco gasification process: (1) Compared with dry feed, the slurry feed system is relatively simpler, safer, and more flexible to operate; it requires less electrical power for the slurry preparation process, there is no risk of coal dust explosions, and no dust emissions are generated by the slurry preparation system. Coal does not need to be dried and can be fed directly into the pulping system. Furthermore, the water-coal slurry feed can handle various materials (coal, petroleum coke, other wastes), offering flexibility in feed types. Furthermore, by using water-coal slurry as the feed, the gasifier can operate at higher pressures (2.5–8.5 MPa), which is essential for certain chemical processes. 　　(2) The gasification furnace operates with a single nozzle, with all the material to be gasified being fed in through this one nozzle. This approach has the advantage of a simple structure, but due to the high local heat load and large flow rate, overheating damage or wear problems are inevitable. To date, the longest cumulative operating time for Texaco gasifier nozzles has been only 3 months before they required maintenance and replacement. 　　(3) The Texaco gasifier is equipped with refractory bricks, has no water cooling system, features a simple structure, and requires a low initial investment. However, due to the high temperature inside the furnace, as well as wear and corrosion, the maximum service life of the refractory bricks on the fire-facing side of the Texaco gasifier is currently only 2 years, while those near the furnace walls have a service life of 5 to 10 years. 　　(4) The graywater from the entire plant can be utilized comprehensively; the water after removing large slag and fine ash is also recycled in the pulp-making system. 　　(5) Due to the short residence time of gas in the gasifier, the carbon conversion rate of Texaco gasifiers is low, generally ranging from 96% to 98%. Due to the high moisture content in water-coal slurry, the O/C ratio during the gasification process is relatively high, resulting in high oxygen consumption; moreover, the moisture content in the gas produced is also high. Compared to dry feeding, cold gas has lower efficiency and a more complex heat recovery system. 　　(6) Compared with other gasifiers, the Texaco gasifier has a larger number of units in large-scale commercial operation and more extensive experience. 　　(7) The availability rate of the Texaco gasifier at the Tampa power plant can reach 57% in 1996 and 78% in 1997. The target for 1998 is 85%, and according to the power plant, this target is expected to be achieved. 1.3 Major problems encountered with the Texaco gasifier at the Tampa IGCC power plant and their solutions (1) Blockage of the slag discharge hopper. The issue was basically resolved by adjusting the operating conditions and modifying some of the pipes. 　　(2) Leakage problems in radiant waste heat boilers and convective waste heat boilers. The main reason is likely high-temperature corrosion; the improvement method is to take protective measures and improve the operating conditions of the gasification furnace. Convection waste heat boilers have also experienced problems such as tube wall leakage and ash accumulation blockage. The improved method is to optimize the operating conditions of the gasification furnace and strengthen inspections and soot blowing. 　　(3) Wear problems in the blackwater and graywater systems. The current approaches involve replacing wear-resistant materials, altering the pipeline structure, and improving the separation of fine ash, but they cannot resolve the issue completely. 　　(4) When the type of coal changes, the parts of the gasifier that are most affected are the slag discharge hopper system and the fine ash separation system, as blockages tend to occur there. The current approach is to control operating parameters, accumulate operational experience, improve the design of the lock-hopper system, and enhance its capacity. 　　(5) The 4 gas-gas heat exchangers located behind the convective gas cooler (2 for raw gas and clean gas, and 2 for N2 and raw gas) suffered from ash accumulation, blockages, and corrosion, which caused pipe leaks and allowed dust to enter the clean gas. This led to severe damage to the gas turbine blades. Cracks were also found in the Y-shaped filters that direct nitrogen and gas to the gas turbine. The main reasons include: a low temperature of the gas entering the designed gas-gas heat exchanger, a small diameter of the heat exchanger tubes, and corrosion caused by water that leaks during shutdown (chloride ion corrosion), among others. At present, there is no good solution, so these 4 gas-to-gas heat exchangers had to be removed and steam was used instead to preheat the clean gas, which reduced the overall efficiency of the plant by 1.5 percentage points. 2 Destec Gasification Process 2.1 Structural Features of the Destec Gasification Process The Destec gasifier is a gasification process that utilizes two-stage oxygen gasification, continuous slag discharge, and refractory bricks installed inside the reactor. 80% water-coal slurry (at a concentration of 67%) and pure oxygen (with a purity of 95%) are mixed together and then injected into the first section of the gasifier. In addition to two water-coal slurry nozzles arranged symmetrically in this section, there is also a fly ash recirculation nozzle at the top of the first section, which brings back fly ash from the dust collector. The vaporization temperature in paragraph 1 is 1,371–1,427 °C, and the vaporization pressure is 2.76 MPa. The crude gas produced in the first reaction stage enters the second gasification zone. The second stage of gasification is a vertical pressure vessel lined with refractory bricks; 20% water-coal slurry is injected through nozzles in this stage, where it mixes with the raw coal gas and undergoes distillation, cracking, and gasification reactions, thereby increasing the calorific value of the raw coal gas while reducing its temperature. At the outlet at the top of the gasifier, the temperature of the gas is approximately 1,038 °C; therefore, only a convective gas cooler is required. The Wabash River IGCC power plant is equipped with 2 gasifiers capable of handling 100% load, one of which is in operation while the other serves as a backup; there is only one set of gas coolers. The gas cooler of this power plant previously had a guide cylinder of the same height as the gasifier, arranged vertically and lined with refractory material. The gas emerging from the draft tube enters a convective gas cooler, where the hot gas flows inside the tubes while water flows outside them, generating saturated steam at a pressure of 11.03 MPa with a flow rate of approximately 90.7–113.4 kg/h. This steam then enters a waste heat boiler for superheating. The gas is cooled to 371 ℃ and then enters the gas dust removal and desulfurization system. The gas cooler of this power plant has a diameter of about 3 m. 　　The water-coal slurry preparation and black water treatment systems of the Destec gasification process are basically similar to those of the Texaco process. 2.2 Analysis of the performance and technical-economic indicators of the Destec coal gasification process (1) By the end of 1997, the Wabash River Power Plant had operated for a total of 4,656 hours, during which 469,220 tons of coal were gasified. The maximum load of the gasifier could reach 100%–103%, while the longest continuous operating time of the gasifier was 362 hours; the efficiency of cold gas production was 71%–74%. The availability rate of the gasifier was 84% in 1996, reached 98% in 1997, and was also 96% in 1998. Of course, this is the data for when one gasification furnace is in operation with another as a backup; when only one furnace is in use, such a high availability rate cannot be achieved. The nozzle life of a gasification furnace is generally 2 to 3 months, while the life of refractory bricks is usually 2 to 3 years; the refractory bricks in Section 2 have an even longer lifespan. 　　(2) The Destec gasifier uses two-stage gasification, which increases the calorific value of the gas, reduces oxygen consumption, and lowers the outlet temperature of the gas. This eliminates the need for large and expensive radiation waste heat boilers, thereby reducing the cost of the gasifier. Moreover, an increase in the calorific value of gas also helps to improve the overall efficiency of IGCC power plants. The calorific value of the gas produced by the Desetc gasifier at standard conditions is approximately 10,425.5 kJ/m3, whereas that of Texaco gas is generally 8,563.8 kJ/m3. 　　(3) The tube-type convective cooler used has low cost and installation expenses, and is easy to maintain and clean. 　　(4) The Destec gasifier uses a pressure screw-type continuous slag discharge system, resulting in lower costs for the pressure relief and slag crushing equipment. 2.3 Major problems that occurred in the Destec gasifier at the Wabash River IGCC power plant and their solutions (1) There were 2 instances of consecutive blockages in the slag discharge outlet. This is due to the presence of many large particles in the water-coal slurry, which causes fluctuations in the supply of the slurry and leads to instability in gasification and blockages. Solution: Strictly follow the operating procedures, control the quality of the water-coal slurry, and ensure stability during the gasification process. 　　(2) Ash deposition in the inlet pipeline of the gas cooler limits the unit’s operating time. The main measures involve improving the size and shape of the coal gas pipeline in front of the convective cooler, thereby increasing the flow velocity of the coal gas and reducing the formation of large deposits in the pipeline; this prevents such large deposits from entering the coal gas cooler along with the gas flow. Additionally, the operating temperature of the gasifier is strictly controlled. For added safety, a filter is installed on the inlet pipe of the gas cooler to prevent larger deposits from entering it. 3 Shell Gasification Process 3.1 Structural Features of the Shell Gasification Process (1) Coal powder preparation and feeding system. The Shell gasification process uses a dry coal powder feeding system. The coal drying and grinding systems are similar to those in conventional power plants, but the feeding system uses high-pressure N2 gas for dense-phase transportation. Unlike water-coal slurry, the entire system must have explosion-proof measures in place. After pre-crushing, it enters the coal drying system to reduce the moisture content in the coal to less than 2%, and then it goes into the coal grinder where it is turned into coal powder. For bituminous coal, the coal powder fineness R90 is generally 20%–30%; the coal grinder operates at atmospheric pressure, and once the powder is produced, it is sent to the coal powder silo using N2 gas. Then it enters the level 2 pressurized lockhopper system. High-pressure N2 gas is then used to deliver the coal powder to the 4 gasification furnace nozzles at a high solid-to-gas ratio; there, the coal powder mixes with oxygen (95% purity) and enters the gasification furnace along with steam to undergo reaction. 　　(2) Gasifier. The mixture of coal powder, oxygen, and steam injected by 4 symmetrically arranged burners undergoes rapid gasification reactions within the gasifier. The temperature in the gasifier is maintained at 1,400–1,600 °C; this temperature causes the ash contained in the carbon of the coal to melt and drip to the bottom of the gasifier. After being quenched, it turns into a glassy, insoluble slag that is then discharged. 　　The raw gas rises with the airflow to the outlet of the gasifier; after passing through a transition section, it is quenched rapidly from its high temperature to 900 °C using low-temperature raw gas that has been dust removed (around 150 °C), and then enters the convective gas cooler. In the transition section with a certain inclination, as the hot gas is suddenly cooled, most of the molten ash contained in it solidifies and falls to the bottom of the gasifier. 　　A vertical tube membrane-type water wall is arranged inside the pressure shell of the Shell gasifier to generate medium-pressure steam at 4.0 MPa. There is a very thin refractory coating on the fire-facing side, which serves to protect the water wall as molten slag flows over it. The gasifier in the Demkolec IGCC power plant has a diameter of about 5–6 meters, a height of over 50 meters, and its elevation reaches over 60 meters. The operating pressure of the gasifier is approximately 2.6–2.8 MPa. 　　(3) Gas cooler. The hot gas is further cooled to around 250 °C in the gas cooler. The low-temperature cooling section generates medium-pressure steam at 4.0 MPa; this steam is mixed with the medium-pressure steam produced by the gasifier, and then together with the exhaust steam from the high-pressure cylinder of the turbine, it is reheated to become medium-pressure reheat steam. The high-temperature cooling section generates high-pressure steam at 13 MPa, which, together with the high-pressure steam from the waste heat boiler, is superheated to become main steam. 　　The gas cooler at the Demkolec power plant has a diameter of about 4 m and a height of about 64 m; the top of the cooler is at an elevation of around 74.5 m, which is the highest point on the gasification island. The pressure shell of the cooler is equipped with 8 layers of coiled tubes, divided into 5 sections vertically; hot gas flows from top to bottom outside the coiled tubes, where it exchanges heat with the water inside them. Each layer of spiral coils is equipped with a pneumatic hammer to knock away dust accumulation. 　　Since the IGCC system consisting of Shell gasifiers uses dry dust removal, its black water and ash water treatment systems are relatively simple; however, its main processes are similar to those of Texaco, so they will not be discussed in detail here. 3.2 Analysis of the performance and technical-economic indicators of the Shell gasification process (1) The CO and H2 contents in the gas produced by the Shell gasifier are much higher than those in the gas produced by the Texaco gasifier, whereas the CO2 and H2O contents are much lower. Due to its high proportion of combustible gases, it has a high cold gas efficiency (about 80%–83%), and IGCC power plants built using this material also achieve a high power generation efficiency (43% LHV). The cold gas efficiency of coal water slurry feed is generally only 74% to 77%. The efficiency of the resulting IGCC is also low (41% LHV). 　　(2) Since the moisture content in gas is low (2.0%), IGCC systems using Shell gasifiers suffer less loss of heat energy from the hot gas due to cooling at normal temperature. In contrast, gas fed into coal-water slurry systems typically contains about 16.8% moisture, so when such hot gas is cooled to normal temperature, a large amount of sensible and latent heat is lost. The water-coal slurry fed gasification process has an even more urgent need for high-temperature purification. 　　(3) The nozzles and water wall of the Shell gasifier have a long service life; no damage has been observed after more than 10,000 hours of operation at the Demkolec power plant, and the availability rate of the gasifier has reached 95%. 　　(4) Due to the use of dry feeding, the oxygen consumption during the gasification process is lower compared to that when using slurry feeding, and the CO2 content in the gas produced is also much lower than that in the gas generated from slurry feeding. For gasifiers of the same capacity, the air separation plant required for Shell gasification can be less than 15%–25%. 　　(5) The use of dry ash recycling improved the carbon conversion rate (which can reach 99%). 　　(6) The dry feeding system is much more complex than water-coal slurry, and its operation and maintenance require stricter controls. The explosion-proof and leak-proof features of the feeding system are extremely important. The land area and construction cost of the feed system are higher than those of water-coal slurry. Furthermore, the dust emissions from the dry feed system are much higher than those from the water-coal slurry feed system. 　　(7) Since the Shell gasifier operates with 4 (or more) nozzles, it can easily operate under both low and high loads, offering great operational flexibility and enabling larger-scale implementation. It is reported that the minimum load of the Shell gasifier can reach 25%, meaning that only one nozzle is in operation. 　　(8) The most important control parameters during the operation of the Shell gasifier are as follows: gasifier outlet temperature ； Syngas cooler inlet temperature ； Gas composition ； Parameters of steam (flow rate, temperature, pressure) ； The amount of slag discharged and its appearance. 　　(9) The load variation rate of the gasifier is greater than 5% per minute, while that of IGCC is approximately 3% per minute. 3.3 Problems encountered with the Shell gasifier in the Demkolec IGCC power plant and their solutions During the operation of the Demkolec power plant, the Shell gasifier and its auxiliary systems functioned fairly well, with a high availability rate. The following problems occurred during the initial operation phase: (1) blockage of the slag discharge hopper ； (2) Fine slag affects the black water treatment system. The causes and solutions for the above two issues related to the gasification process are the same as those mentioned earlier, so they will not be repeated here. 4 Prenflo gasification process 4.1 Structural features of the Prenflo gasification process (1) Powder preparation and transportation system. Similar to the feed system of the Shell gasification process, the Prenflo gasification process also uses a dry feed system. The requirements for the pulverization system are that the coal powder fineness R100 of bituminous coal should be 25%, with a moisture content of less than 2% (by weight) ； For lignite, the coal powder fineness R100 is required to be 25%, with a moisture content of less than 6% (Wt). 　　(2) Gasifier and gas cooler. The Prenflo gasifier is equipped with 4 burners arranged symmetrically. Coal powder supplied from the feeding system is injected into the reaction zone of the gasifier along with oxygen (85% purity) and steam to undergo a reaction. The temperature in the reaction zone is around 1,500 °C, while the temperature at the core of the flame reaches as high as 2,000 °C. The gas contains no excessive hydrocarbons, tar, or phenols. The furnace lining in the reactor area is cooled by water wall tubes, and high-pressure saturated steam is generated, which is connected to the high-pressure steam from the waste heat boiler. 　　The liquid slag discharged from the gasification reaction zone is cooled in the water tank of the slag collector, and large pieces of slag are crushed using a slag crusher. It is then discharged through gate-type hoppers and separated from water; the slag is sent to a slag dump or sold, while the water can be reused. After being formed in the lower reaction zone, the raw gas flows upward; before entering the gas cooler at the upper part of the gasifier, cooled gas that has had its dust removed is used to rapidly cool the hot gas, with the aim of causing the molten ash carried by the hot gas to solidify and fall to the slag discharge port at the bottom of the gasifier. The rapidly cooled gas continues to rise and enters the first-stage gas cooler. The gas first rises from the central cylinder of the cooler to the top of the gasifier, then turns downward and exits from the bottom of the first-stage cooler (i.e., the waist portion of the gasifier) through the annular convective cooling zone between the central cylinder and the furnace walls, entering the second-stage convective cooler. The annular cooling zone of the first-stage cooler is equipped with 4 layers of coiled tube heat exchangers; hot gas flows outside the tubes while water flows inside them, generating high-pressure saturated steam. This is the difference between Prenflo and Shell gasifiers. 　　The structure of the stage 2 cooler is similar to that of the convective cooler in the Shell gasification process. The interior is also equipped with multi-layer spiral coiled heat exchange tube bundles; the spiral coils of the second-stage convective cooler in the Prenflo furnace at the IGCC power plant in Puertollano, Spain, have a total of 6 layers, arranged in 3 groups above and below. After passing through the second-stage cooler, the hot gas is typically cooled to around 250 °C, and saturated steam is also generated in this process. 　　(3) Dust removal and fly ash recycling system. The cooled raw gas passes through a primary dry dust collector (such as a ceramic filter or cyclone separator) to capture most of the fly ash; it is then sent back to the gasification furnace using N2 via a lockhopper, in order to increase the conversion rate of carbon. The raw gas is further passed through a primary water scrubber to reduce the dust content in the gas to less than 1 mg/m3, after which it enters the desulfurization system. 4.2 Analysis of the performance and technical-economic indicators of the Prenflo gasification process (1) The efficiency of the cold gas can reach 80%–83%, while the overall efficiency of the gasifier can reach 95%. Test results on U.S. Pittsburgh No. 8 coal show that when oxygen with a purity of 85% is used as the gasifying agent, the calorific value of the gas, the carbon conversion rate, the cold gas efficiency, and the overall efficiency are not significantly different from those obtained when oxygen with a purity of 95% is used for gasification. Therefore, the Prenflo furnace uses oxygen with a purity of 85% as the gasifying agent. The Prenflo gasifier can achieve a load variation rate of 2% to 15% per minute on a small test bench, with the CO2 content in the gas and the gas pressure remaining almost unchanged. Since 4 burners are also used, at 50% load it can be operated easily with just 2 burners. 　　(2) Operation status of the Prnflo furnace at the IGCC power plant in Puertollano, Spain. Gas power generation began in early 1998, and to date a total of 198 hours of operation has been achieved, with the longest consecutive operating period being 25 hours at a load of 80%. The gasifier operated at 75% load for 40 hours. As of September 1998, there were no records of the gasifier or the entire IGCC power plant operating at 100% load. Tests conducted with a 50% coal and 50% petroleum coke mixture showed that the actual operating data were very close to the design values. From July to August 1998, a major overhaul of the unit was carried out, focusing on the maintenance of the Siemens gas turbines. The unit has been restarted. 4.3 Major problems that occurred in the Prenflo gasifier at the Puertollano power plant and their solutions (1) Poor powder discharge from the pressure-fed hopper. There is a pipe for returning N2 in the level 2 lock hopper; due to the overly small diameter of this pipe, the exhaust of N2 is inefficient, which results in discontinuous descent of the coal powder. The solution is to add a Venturi extractor to the return pipe in order to increase the speed of N2 return, thereby ensuring smooth exhaust and continuous, uniform descent of the coal powder. 　　(2) Fine slag filtration issues in black water and gray water treatment systems. Similar to the problems encountered at the Demkolec and Tampa power plants, the gasification island at the Puertollano IGCC plant also faced issues where an excessive amount of fine slag led to high slag content in the black water, causing wear and blockages in the black water system. The solution to such problems was to use filtration to remove the fine slag from the black water. 6 Conclusions 6.1 The single-furnace capacity of both the water-coal slurry fed gasification processes in the United States (Texaco and Destec) and the dry-fed gasification processes in Europe (Shell and Prenflo) has reached the 2000–2500 t/d range, and IGCC demonstrations on the order of 250–300 MW have been carried out for all of them; all four types of gasifiers employ oxygen-fired fluidized bed gasification technology. This provides a relatively comprehensive range of options for our country to choose from when selecting gasification processes. 6.2 The Texaco gasifier has the most operational experience and the largest number of units in commercial use, being applied in IGCC power generation; its availability rate can also reach over 80%. However, its nozzles and refractory linings have a shorter lifespan, and the efficiency of cold gas utilization as well as the efficiency of IGCC systems remain low at present. If the efficiency of IGCC is designed to be 43% (LHV) using a Texaco gasifier, significant improvements to its waste heat boiler and total heat recovery system are necessary in order to achieve this target. 6.3 Although the Destec gasifier also uses coal water slurry as feed, it features two-stage gasification; its cold gas efficiency is higher than that of Texaco, and it eliminates the need for a radiant waste heat boiler. Additionally, the use of a fire-tube type convective cooler significantly reduces the cost. If combined into an IGCC, many experts believe that an efficiency of 43% (LHV) can be achieved, with relatively low costs. However, compared to dry feeding, its nozzles and refractory bricks have a shorter lifespan. 6.4 The availability rate of the Shell gasifier has reached 95%, indicating that it is now in commercial operation; both its nozzles and water walls have a long service life. The cold gas efficiency and the overall IGCC efficiency are relatively high compared to the wet-fed gasification process; an IGCC efficiency of 43% (LHV) can be easily achieved using the Shell process. But its cost is relatively high compared to Texaco and Destec. 6.5 The Prenflo gasifier is basically similar to the Shell gasifier, with only differences in the cooler design. Due to the short operating time of the demonstration plant in Puertollano, Spain, the performance of the Prenflo gasifier still needs to be tested over time. 6.6 The type of coal has a significant impact on the performance of gasifiers. For the type of coal used in China’s IGCC demonstration power plants, currently only Texaco and Shell gasifiers have experience in gasifying similar types of coal, and this is also very important when choosing a gasification process. 6.7 Based on the operation of the 4 demonstration power plants, the availability rate of the gasifiers themselves is very high (>85%), but the auxiliary systems connected to them represent the biggest obstacle to the availability rate of the gasification unit and the entire IGCC plant. Among them, the slag and black water treatment systems as well as the feeding system have the most problems, some of which remain unresolved to date. This point should be given great attention when selecting a provider for the gasification process; professional manufacturers in this field should be preferred as much as possible. 6.8 Based on the experiences and lessons learned from 4 demonstration power plants around the world, the following principle considerations should be taken into account when selecting the gasification process for China’s IGCC demonstration power plants: whether the maximum output capacity of the gasifier can meet the required levels ； Has similar coal types been gasified? ； Operating time and number of gasifiers with maximum capacity ； Availability of demonstration operation ； Cold gas efficiency and overall efficiency of IGCC ； What problems still exist at present ； Are both the designers and manufacturers of the gasifier and auxiliary systems professional firms?

Compared with atmospheric pressure gasification, pressurized gasification has the following advantages: 1. Higher production capacity and greater gasification intensity； 2. The equipment is relatively small ； 3. No specialized gas delivery equipment is required ； 4. High content of active gas components ； 5. High efficiency in thermal energy conversion, with high calorific value of the resulting gas ； 6. High carbon conversion rate ；