How to configure a 100,000-ton synthetic ammonia compressor

The last edit to this post was made by GreenFieldWalk on 2009-7-2 at 12:22, with adjustments made. For a synthetic ammonia production capacity of 100,000 tons per year, the effective production time should be taken as 300 days per year; the consumption of purified gas should be calculated at 3,000 units (with a margin for safety), and the inlet pressure should be determined based on the purification pressure. 100000/300=333.3. 333/24=13.8. 13.8×3000＝41400. It’s better to choose a larger compressor.

An annual production of 100,000 tons of synthetic ammonia means a daily production of 300 tons. Assuming that 3,300–3,500 M3 of semi-water gas are required per ton of synthetic ammonia, the size of the compressor needed will depend on the specific circumstances. If the capacity of the compressor is too low, energy consumption will be high, there will be more gas losses, and there will also be an increased number of leakage points. The capacity of a single machine is too high, so a failure of that machine has a significant impact on the system’s production capacity; however, it is not necessary to have a separate backup machine for this purpose. Therefore, it is recommended that the poster equip several units with a capacity of over 100 M3, ensuring that the impact of each individual unit on the system’s overall capacity does not exceed 20%. The determination of the inlet pressure depends on the specific process, such as whether it is pressurized conversion or atmospheric conversion, as well as the equipment and process configuration for desulfurization and the final reaction pressure for ammonia synthesis. In the typical processes for ammonia synthesis, the inlet pressure of the compressor is generally around 300 MMHG.

Hello! Compressors equipped for a synthetic ammonia plant with an annual capacity of 100,000 tons. It is necessary to know the source of the feed gas, the gasification method, and the selection of other processes. If the atmospheric pressure gasification process commonly used in current medium-scale ammonia synthesis plants is adopted, 5 reciprocating hydrogen-nitrogen compressors with a gas handling capacity of 11,000 NM3/H will be installed; 4 of these compressors will be in operation while 1 serves as a spare. The inlet pressure at the first stage of the compressor is generally 300 mmH2O after coal gasification. If the system is to be modified to increase production capacity, a coal drum can be added before the inlet of the first compression stage to raise the pressure to 15 KPa, thereby increasing the amount of gas that the compressor can handle.

The inlet pressure for compression cannot be increased arbitrarily; it depends on the system’s operational conditions and the compressor’s load. Otherwise, an excessive load on the compressor can lead to catastrophic accidents.

The inlet pressure at the first stage of the ammonia synthesis compressors in the Shouguang Alliance Chemicals plant in Shandong is 200 mm of mercury, while in our company it is at least 350 mm of mercury, and usually around 400 mm of mercury. Currently, there are 3 MH92 compressors, 1 MH75 compressor, 1 H12 compressor, and 2 6MD110 compressors. Is this configuration reasonable? Our company currently uses fixed-bed indirect gasification to produce synthetic raw gas. Another question is: by how much does each 10 mmHg change in pressure affect the gas production volume (per unit)?

200 mm of mercury is considered normal. For those hydrogen and nitrogen compressors you mentioned, the designed inlet pressure should be 0.25 kg/cm2 (gauge pressure); 200 mm of mercury is roughly equivalent to this value. An inlet pressure of 400 mm of mercury is significantly too high, and it is not favorable for the long-term operation of the machine； There are many types of compressors available, and it’s not the ideal configuration ； Using 350 mmHg as a reference, the increase in volume for every additional 10 mmHg is: 10/(760+350) = 0.9%. Since the water content in semi-water gas is even lower, the actual increase is slightly higher than this value.

For 100,000 tons of synthetic ammonia production, an air volume of around 50,000 cubic meters per hour, or approximately 800 m3 per minute, is required. It is possible to use 3 to 4 compressors, with each compressor delivering 300 m3 or 250 m3 per minute; this results in a total load of 110–120%.

It is recommended to use two 6M50 compressors and one 6M25 compressor, or four 6M25 compressors, to operate without any backup units. One of our company’s units consists of 4 6M50 compressors and 1 6M25 compressor, and it can produce a total of 240,000 tons of ammonia per year without undergoing major repairs. When pressure is applied, it has a significant impact on the volume of air. However, it is necessary to consider various factors. For example, if the design pressure is set at 26 kPa, it is necessary to check whether the pressures at the first, second, and third outlets can reach this design value. If they do not, or if there are large differences between these pressures, the reasons need to be identified. If the issue cannot be resolved, the only option is to increase the inlet pressure. However, it is essential to pay attention to the balance between various sections, to consider the actual operating conditions of the compressor, and to monitor vibration levels and piston movement. The imported pressure from the Shandong factory is generally quite high.

I’m not sure what your ammonia synthesis capacity is, but judging from your compressors it seems to be not very large. The air delivery capacities of the several compressor models you mentioned must be 92, 75, 12, and 110 respectively, right? So your displacement is 92*3+75+12+110*2=583 cubic feet per minute. The factory in Shandong mainly uses lump coal; based on a rate of 3,300 cubic meters of semi-water gas per ton of ammonia, and assuming 300 days per year, the calculation should be 583*60*24*300/3300 = 76,320 tons of ammonia. Is this correct? There’s still a long way to go before reaching one hundred thousand tons.