Report on the Investigation of Shandong Zaozhuang Aixin Si (Zaozhuang) New Gas Co., Ltd

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I. Basic Overview: Shandong Aixinsi (Zaozhuang) New Gas Co., Ltd. is a coal gasification company using the ash pyrolysis method, invested and established by the American USS Company. The total investment amounts to approximately 160 million RMB, with a workforce of 160 people. The company operates two sets of ash pyrolysis units, whose combined capacity for producing gas equivalent to methanol is 100,000 tons per year; each unit has an annual production capacity of around 50,000 tons. The core technology used is that of the American UGI Company, and in terms of the process flow, it is basically similar to the technology employed by the Shanxi Coal Chemistry Research Institute. The gas produced by this company is mainly used by Haihua Company (formerly Zaozhuang Coking Plant) for methanol production. The facility was designed by the Design Institute of Shanghai Coking Plant; currently, American companies are not involved in its management, and it is primarily managed by Shanghai Coking Plant. The company has only a supply relationship regarding raw gas with Haihua Company, and it makes use of some of Haihua Company’s utility resources. Looking at the historical development, in 1986, the American company USS built a ash pyrolysis unit at the Wujing Chemical Plant in Shanghai. However, due to engineering flaws, the unit did not operate properly and was later shut down and dismantled. In recent years, as international oil prices have risen, this American company has decided to restart the project, making certain improvements to the original unit before rebuilding it. The company originally planned to use high-sulfur bituminous coal produced locally in Zaozhuang; the designed sulfur content in the gas produced was 15 g/M3. However, since there was no capability to remove such a high level of sulfur from the gas at the time of operation, the sulfur content of the coal actually used is not at the designed level. Currently, coal from Yima, Henan Province, is being used, and its calorific value is approximately 4500–5500 kcal. (The company does not analyze each batch of coal.) This coal has a low carbon content of around 55%, high volatiles, and high ash content. This coal has poor slurry-forming properties, with a ash fusion point (T2 temperature) of around 1250 degrees. II. Operation status: Since 2007, this unit has been in operation intermittently for nearly a year, with multiple periods of shutdown in between. The longest continuous period of operation was 47 days. The most recent start-up of this unit was at the beginning of December, and it has been running for over 20 days since then. In terms of continuity of operation, it is possible to maintain continuous operation, but the unit itself has various issues as well. The process of this device consists of coal transportation, coal drying, coal gasification, dust removal and slag discharge, as well as waste heat recovery. Desulfurization, decarburization; utility services include air separation, water supply, gas supply, etc. The details are as follows: The company uses pneumatic conveying for transporting coal, and there is no principle-related issue with this method. Since the equipment is installed at a relatively low height, the ceiling height of the factory building is also low – roughly about ten meters lower than that of our company’s current ash pyrolysis facility. See the panoramic photo in the attachment: (the steel structure building in the image is the gasification island). There is no issue with the airflow transportation technology itself, but due to the uneven particle size of the raw coal, blockages often occur. The final dust treatment stage in pneumatic conveying uses a bag filter. The drying of the raw coal is carried out using a drum dryer, with nitrogen being used as the drying inert gas. For safety reasons, the oxygen content in this inert gas is strictly kept below 3%. (The left side of the image above shows the drying building, with part of it being the control room.) The heat source for drying is gas produced by the combustion of coal gas, which comes from the coke oven gas of Haihua Company. Since the calorific value of the gas generated through gasification is low, the company’s own produced gas was not used for drying purposes in the design. From the perspective of drying itself, there isn’t much of a problem. The process of the gasification island itself is basically the same as that of our company’s current units, but the structure of the gasification furnace differs significantly; the furnace has an expanded section, with a diameter of φ2600 in the lower dense-phase zone, and a diameter of φ3600 in the expanded section of the upper dilute-phase zone. Its principle is designed to reduce the flow velocity at the upper part, thereby minimizing the amount of material carried away. However, based on actual operation, the effects are not significant. For dry dust removal in this device, dry cyclone dust removal is used. Judging from the return material from the dust collector, the return material from the first cyclone is satisfactory, while that from the second and third cyclones is very poor, which also has an adverse effect on the subsequent systems. It is also one of the reasons for high device consumption. After dry dust removal, waste heat recovery is carried out to generate steam. The gas inlet temperature is around 850 degrees, while the outlet temperature is around 230 degrees. The operational data can be found in the operation record sheet. Since there is no flow meter, it is not possible to measure the amount of steam generated by waste heat recovery. However, by calculating based on the total volume of gas and the temperature drop (from 800 degrees to around 200 degrees), it can be estimated that the amount of steam produced is roughly sufficient to meet the demand. Due to the unsatisfactory dust removal through centrifugation in the previous process, dust accumulates in the evaporation zone and superheating zone of the waste heat boiler during each inspection. After dry dust removal, wet dust removal is carried out, which consists of two stages: one is the dust removal tower and the other is the water cooling tower. Based on observations on site, the effectiveness of wet dust removal is not satisfactory, as evidenced by the high amount of ash present in the sulfur paste produced by the subsequent desulfurization process. Analyzing the reasons for inadequate dust removal, it is mainly due to the poor effectiveness of dry dust removal in the previous process. Due to the high sulfur content in the design gas, desulfurization is carried out in three stages; the design for this desulfurization process was developed by Hangzhou Warner Company. However, since the sulfur content in the gas is only around 6 grams per cubic meter, one stage of desulfurization is sufficient to meet the requirements. The actual desulfurization results are shown in the attached analysis records: As can be seen from the records, the hydrogen sulfide content in the inlet gas was nearly 6 grams, while it dropped to around 22 mg in the outlet gas; considering the desulfurization efficiency, it is quite good. The problems with desulfurization are inadequate regeneration, a short residence time in the regeneration tank, and a high level of suspended sulfur in the desulfurization liquid. The decarburization is carried out using pressure swing adsorption; in terms of decarburization efficiency, it is fairly satisfactory. However, from the perspective of the gas composition analysis, due to the low operating pressure, hydrogen loss remains high despite the use of vacuum desorption. Up to over 3% of the hydrogen in the desorbed CO2 gas can be recovered. III. Advantages and disadvantages Advantages: 1. The device can operate continuously in most cases. It can produce qualified gas. The effective content of the purified product gas can reach over 86%, making it suitable as steam for ammonia and methanol synthesis. 2. It is possible to use low-quality coal; the original design specified a sulfur content of 15 grams in the gas. Although the actual operating conditions do not meet this standard, the fact that installing just one desulfurization tower is sufficient to reduce the sulfur content from 6 g to 22 mg shows that there is considerable capacity for desulfurization. 3. It can use low-quality coal as raw material. Disadvantages: 1. High consumption – over 1 kg of coal is required per cubic meter of effective gas; based on this, nearly 3 tons of raw coal are needed to produce one ton of methanol. 2. The pressure cannot be increased to the desired level. The original design called for a pressure of 1 Mpa, but in practice the pressure is only 0.25 Mpa. The company is hesitant to increase the pressure or temperature further, fearing that this could lead to serious accidents if the furnace operates at higher levels. As a result, the temperature in the dense-phase section of the gasifier never exceeds 1000 degrees, which prevents the ash from forming balls and leads to increased consumption. Production capacity has declined. 3. The return of the ash separated by the cyclone separator to the gasification furnace is not satisfactory; the first stage of separation works fairly well, but the subsequent two stages are practically unable to handle this ash – the amount carried away exceeds 20%, and according to the company’s technical staff, it can even exceed 30% in some cases. Unless this problem is resolved, the issue of high consumption cannot be addressed. 4. Due to the low operating pressure, the configuration of the subsequent system, especially that of the compressor, becomes a problem; as a result, the gas sent to Haihua is also depressurized to atmospheric pressure before being fed into the gas storage tank, which leads to higher energy consumption. 5. The proportion of non-active gases in the gas is high, especially CO2 and methane. 6. The high-temperature valves in the ash discharge system, although they are imported products, begin to operate slowly and fail to close properly, resulting in leaks. As a consequence, it is difficult to maintain the system pressure, which prevents the system from reaching the required operating level. This is also one of the bottlenecks in this project. 7. The company did not design a system for treating the dust removal water; as a result, the turbidity of this water is very high, which in turn leads to poor dust removal efficiency. The company is now taking corrective actions to upgrade the water treatment system. In discussions with the company’s technical staff, they explained that the company incurs losses of over 3 million per month at present. When asked how to address these issues, they suggested that the problem lies with the gasification furnace; while its long-term operation is not an issue, high energy consumption is a serious problem. The reasons for this high consumption are related to both the furnace itself and the operating pressure. If these two problems are resolved, production capacity will increase and other issues will gradually improve. However, so far no breakthrough has been achieved in terms of raising the temperature and pressure of the furnace. Another point that requires our close attention is the issue of coal quality compatibility. They believe that this furnace does not have the same level of adaptability to different types of coal as originally thought; there are specific requirements regarding the T2 temperature. If T2 is too high, the coal remains at its deformation temperature and cannot aggregate into balls. If T2 is too low, it may reach the flow temperature, which could deteriorate the operating conditions of the gas generation furnace – the coal will stick together to form large clumps, worsening the flow conditions and leading to blockages. In addition, the company plans to build large-scale facilities in Inner Mongolia Autonomous Region and Henan, where the coal quality is worse and the designed hydrogen sulfide content in the gas is as high as 21%, but the project is still in the preliminary stage.