Seeking small-scale technical improvement measures for gasification units

Let me start with two to lay the foundation, 1. Reasons for and solutions to the control improvement of the gasifier outlet temperature: During the commissioning phase, it was found that the temperature of the syngas at the gasifier outlet exceeded the design value and could not be effectively controlled, especially under high load conditions; as a result, the gasifier could not operate at the designed load level and had to maintain production at lower loads. According to calculations by Shell’s experts, the best and most effective approach is to inject some of the boiler water into the low-temperature steam generator (E1303D); the specific plan is currently provided by SHELL. Consider: ① Implement separate water supply for the system; ② Lower the temperature of deoxygenated water; ③ Consider reducing the oxygen content requirement. 2. Improvement plan for temperature control of the low-load bed in R2301: During the CO conversion process in the shell gasification purification stage, it was found through trial operation that, when R2301 is operating with air introduction or at low load, its bed temperature is difficult to control using the current adjustment methods, and over-temperature conditions occur very easily. To effectively control the temperature of bed R2301, ensure the catalyst’s service life, and prevent equipment damage, it is recommended to install a gate valve at the inlet of the tube side of 2302. When the inlet temperature of R2302 is high, this valve can be appropriately closed to allow a certain amount of syngas to pass directly through 23TV003 and into R2301 without going through E2302 for heat exchange, thereby achieving control over the temperature of the bed in R2301. Solution: Add a gate valve on line 500-PG-23009 in the inlet tube side of E2302. This post was last edited by Ma Hai on 2009-4-11 09:51]

Excerpt: The author recently visited a calcium carbide factory in a coastal city in Liaoning Province for an investigation. It is a small factory; the total number of employees there is 96, and it has only one calcium carbide furnace with a capacity of 1350 kVA. At first, they did not understand the production process; they purchased raw materials (lime and coke) from outside and fed them into the electric furnaces without any processing. A high voltage was used, and the operation was essentially carried out with an open arc. The electricity consumption per ton was over 4,000 units, and the quality of calcium carbide was poor. Later, they learned from the experiences of other factories and installed a set of raw material crushing and screening equipment to crush coke to 3–12 millimeters and lime to 5–25 millimeters. The secondary voltage decreased from 84 volts to 70 volts, while the secondary current increased from 10,400 amperes to 14,000 amperes; the overload operation reached 1,969 kVA. They also use manual feeding on the furnace surface; there are five furnace operators, who work under a responsibility system, with each person in charge of one furnace. The work on the furnace surface was carried out with great care, eliminating any possibility of arc formation; as a result, excellent results in terms of high output, high quality, and low consumption were achieved for three consecutive years. The entire plant earns 390,000 yuan per year (as power supply is limited, it can only operate for half a month each month). It is no easy task to achieve arc closure operation on such a small calcium carbide furnace. In the past, the author has written books on calcium carbide production, always believing that arc operation in small calcium carbide furnaces is inevitable, especially with such small-scale furnaces. After seeing this small electric furnace, while writing this book, the author wants to tell readers that regardless of the size of the furnace, appropriate measures can be taken to ensure arc closure operation, thereby achieving good production results.

The circulating cooling pumps originally used in our gasification workshop were imported models equipped with double-end face mechanical seals, which did not perform well – these seals tended to break frequently. Additionally, the heat transfer oil used to cool the seals was very expensive, resulting in extremely high costs. Now we are using domestically produced pumps with single-end face mechanical seals, which are cooled by gas and water; they are not only more durable but also eliminate the need for heat transfer oil, which is great.

The high-pressure flash steam from gasification contains a large amount of ash, which leads to ash accumulation on the shell side of the ash water heater and affects the heat exchange efficiency of the heat exchanger. Subsequent calculations (based on HG/T 20570.8-95 for the design of gas-liquid separators) showed that the diameter of the high-flash equipment and the height of the vapor phase were insufficient, resulting in the flash vapor containing ash and water. Subsequently, newly manufactured high-flash equipment was installed during a major overhaul, which basically eliminated the issue of flash steam carrying ash.

Our plant’s nitrogen venting system was originally designed with a single L-shaped vent path; it was later found that the backpressure after venting was extremely high, causing severe distortion of the pipes. After switching to a T-shaped vent system with two paths, this issue has not occurred again.

Previously, while working at a factory learning about Texaco processes, it was found that the pipeline through which the black water from the vacuum flasher in that factory was sent to the sedimentation tank often got clogged. The operators would take turns using hammers to strike that pipeline; as a result, the pipe became distorted. This task was extremely difficult for the operators, and it was also impossible to control the liquid level. Research has shown that this plant’s true flash line is equipped with a set of automatic control valves (whose purpose is to regulate the level of the true flash liquid); it is mainly blockages at this location that cause problems. Additionally, the diameter of this pipeline is also relatively small (DN150). Later, during the installation at our factory, all valves on that pipeline were removed, and the pipe diameter was increased to DN350; the outlet was connected directly to the sedimentation tank, using the water in the tank for liquid sealing. As a result, after nearly a year of operation, it has never gotten clogged. The renovation was a success.

During normal operation, 13Fv0011 will close, and the temperature of the fluid in the pipelines before and after the valve will drop due to the lack of flow, which can lead to dew point corrosion. When there is a risk associated with the leakage of process gas, this will result in a shutdown of the system. An additional 1″ feed line was added to 13Fv0011; it remains fully open during normal production, **reducing the risk of corrosion and ensuring smooth operation of the production process.

During normal operation, 13T0020 is unable to reach its designed operating value, which poses a risk of corrosion to the downstream pipelines and equipment K-1301. Once the K-1301 fails to operate due to equipment issues, the entire gasification unit cannot function. Add a 4″ feed line to 13Tv0020 to increase the flow of high-temperature gas, thereby enabling 13T0020 to reach its designed operating value. Modifications were carried out when a parking opportunity arose, and by driving again, 13T0020 was reached at the designed operating value.

Before the modification of the accident liquid nitrogen pump 01P801, the return line was located behind the check valve; as a result, when the pressure PI01804 behind the check valve V01842 was higher than the outlet pressure PI01808 of the accident nitrogen pump, it was easy for the liquid nitrogen pump to become blocked, leading to damage due to excessive pressure. Therefore, the return line was moved to be located in front of the check valve V01842, so that when the pressure PI01804 was higher than PI01808, the liquid nitrogen pump could return to the liquid nitrogen tank through the return line.

The backflow gas temperature for S-1501 was low due to shortcomings in the original design; it failed to reach the specified temperature requirements. This low backflow gas temperature posed a risk of damaging the ceramic filter rods, which are key components inside S-1501. Therefore, as an improvement, an 1-inch vent was added from S-1501 to the nitrogen vent silencer on the 86m platform system, in order to raise the backflow gas temperature. As a result of this technical modification, the backflow gas temperature increased from 130 degrees to around 192 degrees, bringing it closer to the designed value and thus ensuring the safety of the filter rods. It ensured the normal operation of S-1501.

The original Texaco unit had a sedimentation tank feed pump; raising the true flash point eliminates the need for this pump

The filter element inside S-1302A/B is made of sintered metal, with a pore size of 5um. When the pressure difference across the filter becomes high, if backwashing is not carried out in a timely manner, the flow rate of water used for temperature control in the coal burner of the gasification furnace will gradually decrease, thereby affecting the stable operation of the equipment. It is necessary to remove the filter and its element; having a professional company clean it does not yield satisfactory results. Replacing the element is too costly, and each cleaning process also requires the replacement of gasket seals, which wastes labor and financial resources. By introducing a nitrogen backwashing process, it becomes possible to remove the filter for online backwashing when the pressure difference is not too high. This eliminates the need to open the filter’s cover, yields better results, and also extends the lifespan of the filter element.