Fast way to stabilize the compression process

Explosion-proof requirements for H2 content The intermediate product methylammonium formed during urea synthesis is highly corrosive to high-pressure equipment. Although urea high-pressure equipment uses urea-grade stainless steel, it is necessary to add an appropriate amount of anti-corrosion air to utilize O2 in air. The passivation film formed on the surface of the stainless steel achieves the purpose of protecting the device.

The volume fraction of H2 in the raw material CO2 provided by synthetic ammonia is as high as 1.1%. After the cyclic reaction in the urea synthesis high pressure ring, the gas phase group formed by H2 and O2 in the added antiseptic air washed by the methylammonium solution at the top of the high pressure scrubber. The fraction is within the explosion limit of H2 (4% 74%). In order to eliminate the hidden danger of explosion, a dehydrogenation reactor was installed in the second stage of the compressor in the process design of Stymika. The catalyst was packed inside, the active component was P, the mass fraction was 0.3%; the carrier was Al2O3; 3mm. Through the dehydrogenation reactor, H2 in the feed gas CO2 and O2 in the added anti-corrosion air are reacted under the condition of 185, so that the feed gas outlet temperature rises by about 45, and the H2 content is lower than 5010-6, to ensure The gas phase at the top of the high pressure scrubber is outside the explosion limit. At the same time, the volume fraction of O2 is required to be 0.65% of the total feed gas after dehydrogenation.

Normal production conditions From November 2001 to April 2002 (the actual operation time was only 2 months), the catalyst was first loaded and used, and the dehydrogenation effect was good. At full load, the bed resistance drop is stable at 5560 kPa, and the bed inlet and outlet temperature rise is at 3050, which fully meets the design requirements. The H2 content corresponds to the temperature rise of the bed inlet and outlet.

Correspondence between H2 content and temperature rise of bed inlet and outlet. Under different production loads, the inlet pressure of the compressor is 0.165MPa (absolute), the temperature is 40, the volume fraction is 98.5%, and the outlet pressure of the compressor is 14.5MPa. The water temperature is basically constant, and the compressor is always maintained at a relatively low speed to satisfy the suction and pressurization of the gas. See the corresponding relationship between production load and compressor speed and steam usage when the differential pressure is normal (70 kPa).

When the pressure difference is normal, the relationship between the production load and the compressor speed and steam usage is problematic. The resistance increases rapidly. The dehydrogenation catalyst may cause the long-period operation of the crushing device from October 2002. The dehydrogenation reactor of the CO2 compression system is continuous. After running for 1012d, the bed resistance began to accelerate steadily, from the initial daily increase of 35kPa to the late daily 10kPa. When the continuous operation is close to 1 month, the bed resistance of the dehydrogenation reactor reaches 220240 kPa, which exceeds the designed maximum bed resistance of 150 kPa. If it continues to operate, it will further increase the bed resistance, which may cause catalyst cracking and shorten catalyst use. life.

The compressor's air volume decreased, the speed increased, and the steam consumption increased. After 1012 days of continuous operation of the dehydrogenation reactor, the bed resistance began to accelerate steadily and the compressor's pumping capacity decreased significantly. The main performance is that the same amount of CO2 gas cannot be inhaled at the same speed compared with the initial stage of operation; if the same production load is to be maintained, the compressor speed must be increased and the steam usage should be increased. When the bed lamination is lowered at 150220 kPa (abnormal), the correspondence between the production load and the compressor speed and steam usage.

The reason for the rapid increase in the lamination of the dehydrogenation reactor bed was that during the continuous production process in July 2002, it was gradually found that after 1015 d of operation, the bed lamination of the dehydrogenation reactor started at 35 kPa per day, and later in each The speed of 810 kPa is increasing, and the design value of 150 kPa is rapidly exceeded, reaching 220240 kPa. Through the analysis of urea and ammonia synthesis process, the reason for the rapid increase of pressure drop is that the synthetic decarburization regeneration system is running poorly, and the top of the regeneration tower is The washing device can not completely recover the potassium carbonate in the CO2 gas phase, and the trace amount of potassium carbonate powder enters the CO2 compressor with CO2 gas for a long time, and is blocked by the catalyst when flowing through the dehydrogenation reactor, with the increase of deposited potassium carbonate. Forming a dense covering on the upper layer of the catalyst, blocking the passage of the gas, increasing the bed lamination drop, increasing the difficulty of the compressor to pump CO2 gas; meanwhile, there may be a small amount of potassium carbonate in compression The dirt formed on the impeller reduces the flow cross section of the impeller and further affects the amount of air blown by the compressor.

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