Operational summary of the 5 Shell coal gasification units currently in operation in China

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This post was last edited by percy on 2015-11-20 at 20:10. 1. Dear colleagues, please describe the operating conditions of the Shell gasifiers. 2. It is hoped that the shared information will serve as a reference for those who will later utilize Shell technology. The five Shell coal gasification units currently in operation in China are all used to produce feedgas for ammonia synthesis. Among them, the Hubei Shuanghuan gasification unit, which has been in operation the longest, has now been running for 1.5 years; the Liuzhou Chemical gasification unit, which was put into service most recently, has been operating for 10 months. Since Shell’s gasification technology is being used for syngas production for the first time, and also for the first time in China, it presents a great many challenges. During the design, procurement, construction, commissioning, and other phases of the first batch of coal gasification projects, many unforeseen difficulties arose; however, they were all ultimately resolved through the joint efforts of all parties. These valuable experiences, which embody the wisdom of all parties involved, will serve as excellent references for Shell’s gasification projects that are already in operation or about to be launched. They will also provide more comprehensive guidance and a model for Shell’s gasification projects currently under construction or yet to be built. The Hubei Shuanghuan gasification unit was integrated into the plant’s overall production system just 5 hours after it was started up for chemical processing. Within less than 24 hours of operation, the production load reached 80%, and the volume fraction of the useful gas components (CO + H2) reached 80%. Less than 2 months after the start-up of the chemical plant, the production load of the gasification unit reached 100%; the concentration of the active components (CO + H2) remained above 82% despite the poor quality of the coal, while the carbon content in the coal ash was below 1.6%. The Hubei Shuanghuan Shell gasification unit achieving full-capacity operation in such a short time, with all performance indicators reaching excellent levels, represents a remarkably successful outcome compared to the application of all other gasification technologies. For example, it took over a decade of efforts in China to bring the first set of Lurgi gasification units up to basic design specifications ； The first set of water-coal slurry gasification units in China also went through several years of difficulties before achieving stable full-load operation. After more than a year of operation, the Hubei Shuanghuan gasification unit has seen gradual improvements in process control, with various technical upgrades being implemented to enhance its performance; production operations have become increasingly stable, and the unit has been operating at full capacity throughout this period. In 2007, there were 7 shutdowns in total, with the cumulative downtime lasting just over 20 days. From February to September 2007, the operation rate of the gasification unit reached 93.5%, the highest among the 5 gasification units in operation in China. Moreover, the downtime for maintenance was significantly reduced, and the continuous operation time of the unit increased gradually. It operated continuously for 53 days from March to April, 47 days from May to July, and 57 days from July to September. After successfully implementing the project to replace synthetic ammonia feed oil with coal, Hubei Shuanghuan is able to save over 1.1 million yuan in production costs per day, achieving significant economic and social benefits. Since the successful commissioning of the gasification unit at Sinopec Shell Yueyang Company following its first feed-in, the unit has been started and stopped a total of 13 times, with the longest continuous operation period lasting 49 days. Starting in May 2007, the operation of the unit improved significantly, with an operational rate of 62% by July. Before March 2007, the gasification unit of Sinopec Hubei Branch did not operate satisfactorily; for most of the time, it was undergoing rectification and defect removal. Since the modification of the flame shield for the coal burner, the operation of the unit has improved. From April 7, 2007, when materials were fed in and the plant was started up, it operated continuously for 32 days until May 9. In June and July, the plant’s operation rates reached 67.45% and 84.62% respectively; the longest continuous operating time of the plant was 37 days, and the maximum load on the gasifier was 77%. Before April 2007, the coal gasification unit at the Anqing Branch of Sinopec was also under rectification for most of the time. A significant improvement occurred starting in April 2007, and by October 8, the unit had been operating continuously for 60 days. Since its commissioning, the unit has undergone 13 shutdowns (6 in 2007). According to the classification of shutdowns, external factors account for only 23%, while internal factors account for 76.92%, making them the main factors affecting the long-term operation of the facilities. In shutdown incidents caused by internal factors: ① Equipment-related issues account for 60%. These primarily include slag blockage due to leaks in the burner flame shields, malfunctions of machinery and pumps, failures of the chilled gas compressor inverter or high inlet pressure differences, and damage to high-temperature and high-pressure ceramic filters ； ②Operation issues account for 30%, mainly focusing on liquid level control in the slag and water system ； ③There was only 1 instance of shutdown due to interlock activation caused by instrument malfunction. The load is constrained by overheating due to ash accumulation in the gasifier synthesizer cooler as well as by the effects of subsequent processes; the oxygen load in the gasifier remains at around 60% to 77%. Since its commissioning on January 8, 2007, the Liuhua gasification unit has experienced 8 shutdowns; the longest continuous operating period for the unit was 30 days. There were many periods of downtime for maintenance, and it operated at its designed full capacity, with stable production throughout its operation. Although the five Shell coal gasification units that have been put into operation have not been able to operate stably over extended periods due to various reasons—with the longest continuous operating time being just over two months for some units (in several cases, this was due to problems encountered in air separation units and rectisolve units)—the issues arising during their operation have now been or are currently being resolved. With the accumulation of operational experience, the goal of achieving full-load, compliant, and stable long-term operation of these coal gasification units can be realized very soon. Precautions for engineering applications 1. Problems encountered during commissioning or operation: China’s first batch of five Shell coal gasification units were put into service within an 8-month period. Each unit experienced certain problems, to varying degrees, during commissioning and operation. The main problems are: ① Poor airtightness of the coal grinding system ； ②The insulation effect of some steam tracing/electrical heating equipment and pipelines is poor ； ③The diesel system is not clean; the oil system pressure is insufficient and unstable ； ④The reducer after the pressure relief pipe on the pulverized coal circulation pipeline is prone to wear through ； ⑤Fault in the external power, steam, and water supply system ； ⑥Inflation cone blockage and rupture ； ⑦Ignition burner tip is damaged ； ⑧Coal burner cover damaged ； ⑨Fault in the quench gas compressor; the quench gas compressor system has weak resilience to external fluctuations ； ⑩Deformation and damage of the inlet filter of the boiler feedwater circulation pump ； 11 Factors such as impurities in the coal powder can cause fluctuations in the coal powder flow rate or frequent coal changes, leading to unstable operation of the gasifier ； 12 The slag protective layer inside the gasification furnace is unstable, and it is difficult to accurately and visually determine the thickness of the protective slag layer on the inner wall of the gasification furnace ； 13 Fault in the wastewater treatment system; blockages in the equipment and pipelines of the sludge water system ； 14 Slag extractor chain break ； 15 Damage to the internal components of the fly ash filter ； 16 Damage to the quenching zone of the vaporization furnace ； 17 The water inlet nozzles of the gasifier water wall are blocked by foreign objects ； 18 Soot accumulation in the syngas cooler. 2 Issues to be noted and corresponding solutions: Based on an understanding of Shell’s gasification technology and an analysis of the causes of problems encountered during the operation of the five Shell gasification units currently in service, it is necessary to properly address the following issues in the operation of existing Shell gasification projects, as well as in the construction and operation of future Shell gasification projects. (1) Maintain good flowability of the pulverized coal and stable conveyance; otherwise, bridging and blockage of the aeration cones may occur. This can also make it difficult to control the O/C ratio entering the gasifier, leading to a series of consequences. Points to note: ① Keep the moisture content of dry coal powder between 1% and 2% ； ②Ensure that coal powder is not stored in a nitrogen-filled container for too long (less than 10 days) ； ③Ensure proper insulation for the dry coal powder system, so that the coal powder temperature remains above 80 ℃ ； ④Control the particle size of the coal powder after grinding, ensuring that the proportion of coal powder with a particle size of less than 5 μm is less than 10% ； ⑤Add fiber screens to prevent foreign substances from entering the coal powder (this also helps prevent clogging of the coal powder control valves) ； ⑥Control the balanced pressure to prevent poor discharge of V-1204 due to coal powder compaction ； ⑦Control the slow pressurization of V-1205 to the operating pressure of the gasifier + 0.8 MPa, ensuring adequate filling of the aeration cone in V-1205 and preventing compaction of the coal powder therein ； ⑧Pay attention to the installation and initial calibration of the coal powder mass flow meter. (2) Preventing damage to inflation equipment ① Control the pressure difference at the cone section to avoid excessive pressure differences ； ② For V-1204, the amount of N2 entering the inflation cone should be controlled, or its structure should be modified by replacing the sintered metal structure with a porous plate structure. (3) Ignition burner, startup burner ① Pay attention to the installation of the ignition burner and the startup burner to prevent mechanical damage to the burners or damage to the water wall of the gasification furnace ； ② Keep the pilot burner and startup burner passages clean to prevent damage to the burner nozzles or blockages in the passages ； ③A gas buffer tank should be installed on the oxygen main to prevent shutdown of the burner when the first coal burner comes online ； ④Make sure to check the consistency between the manufacturer’s control system and the device’s control system. (4) The reducer pipe followed by the reducing elbow on the coal powder circulation pipeline is prone to wear and damage; it can be replaced with an elbow of a special design. (5) Boiler feedwater and circulation system ① Ensure the effective filtration area, filter mesh pore size, and pressure difference of the filter at the inlet of the boiler feedwater circulation pump to avoid damage ； ② Ensure the quality of the boiler feed water to prevent scaling, which could cause damage to the water wall tubes and the boiler feed water circulation pump ； ③It is essential to ensure the reliability of power supply for the boiler feedwater circulation pump; in the event of a sudden power outage, it can prevent heat from the water-cooled walls at the bottom of the gasifier from being removed in time, leading to damage to those water-cooled wall tubes ； ④During equipment manufacturing, pipe installation, and individual commissioning, care must be taken to maintain the cleanliness of the system, so as to prevent blockage of the LAMONT orifice nozzles and subsequent damage to the water wall tubes. (6) Coal burner: ① To prevent damage to the cooling jacket and expansion joints of the coal burner, double-sided welding on the burner cover must be ensured during assembly, and the expansion joints should be filled with refractory material ； ②Temperature measurements have been added at the inlet and outlet of the coal burner cooling water to facilitate real-time monitoring of the coal burner. (7) Preventing damage to the coal burner cover ① Pay attention to the length of the coal burner extending into the gasifier ； ② Appropriately increase the flow rate of cooling water for the burner shield ； ③ Maintain the stability of the coal powder conveying system ； ④ Maintain stable coal quality (if changing the type of coal, it is necessary to adjust various relevant process control parameters promptly) ； ⑤Pay attention to the addition of vaporized and temperature-regulated steam ； ⑥Appropriately reduce the oxygen-coal ratio ； ⑦The viscosity of the slag is adjusted by the amount of flux used. (8) Gasifier temperature control: The temperature control of the gasifier is now based on the amount of steam generated by the gasifier (with a response time of just a few seconds), while the outlet CO2 concentration serves only as a backup control mechanism (with a response time of 5–10 minutes). Pay attention to the relevant measures that should be taken to ensure the accuracy and stability of the steam flow measurement generated by the gasification furnace. (9) Preventing damage to the quenching zone of the gasification furnace: When the quenching gas compressor fails or the amount of quenching gas is insufficient, it is necessary to ensure an adequate supply of ultra-high pressure N2 to purge the quenching zone of the gasification furnace (via interlock control), in order to prevent damage to that zone. (10) Prevention of slag formation and blockage in the slag-water system: ① To prevent the formation of large amounts of slag and avoid blockages in the 1400 system, it is necessary to measure the composition of ash when changing the type of coal, and determine the amount of limestone to be added through viscosity-temperature tests. ②Pay attention to the changes in viscosity and density of the slurry water in the 1400 system, and increase the amount of circulating water discharged as appropriate to prevent the pipeline system from becoming clogged due to too high a slurry concentration. (11) Tracing of equipment and pipelines: Pay attention to proper tracing of equipment and pipelines in the pulverized coal system, quench gas compression system, and fly ash system. (12) Fly ash filter ceramic tubes: To prevent damage to the ceramic tubes of the fly ash filter, it is necessary to strengthen the connection between the venturi and the tube sheet, and install connectors between the venturi and the backflow pipe openings. (13) CO2 pressurization and transportation: For Shell’s coal gasification project used for methanol production, since CO2 is used to replace N2 as the medium for pressurizing and transporting coal powder, there is currently no existing experience to draw on, and attention should be paid to the range of issues that may arise as a result. (14) Other issues to consider in project construction: ① The supply and installation of the gasifier are the most critical aspects of the Shell gasification project; handling these related tasks properly will help to shorten the project construction timeline ； ②Increasing the number of qualified suppliers for key equipment in Shell’s gasification plants, accelerating the localization of such key equipment and instruments, and speeding up the optimization of the plant systems all contribute to reducing the investment required for plant construction ； ③Tasks such as the clean installation of the vapor system in the gasifier, heating up the refractory lining inside the gasifier, debugging of the constant-force crane, testing the vapor system, single and combined testing of the instrumentation and control systems, and the mechanical completion inspection of the installation are all very important and require special attention ； ④The coal grinding and coal drying systems should be built before other processes, so that qualified coal powder can be produced first and the coal powder flow measurement system can be calibrated; this will create the conditions necessary for feeding chemical materials into the gasifier ； ⑤The quenching process in Shell’s gasification technology offers relative advantages over the waste boiler process for producing synthetic ammonia feed gas, and relevant parties should have high expectations in this regard.