Methyldiethanolamine desulfurization process

1. The crude material gas is subjected to the second stage solvent scrubbing absorption tower at 2.8MPa, the lower stage is absorbed with the solvent desorbed by the reduced pressure flash evaporator to improve the purity of the gas, and the upper stage is then scrubbed with the solvent reconstituted by steam heating. The rich liquid discharged from the absorption tower is successively decompressed through two flash evaporator tanks, and the energy of the first decompression of the solvent is recovered by the turbine. The recovered energy is used to drive the semi-lean liquid circulating pump. The rich liquid contains more hydrogen and ammonia in the steam released from the high-pressure flasher tank, which can be compressed and sent to the decarburization tower. After the solvent in the high-pressure flasher tank is continuously decompressed, it releases a large amount of hydrogen and ammonia in the low-pressure flasher tank. Most carbon dioxide. Most of the obtained semi-lean liquid is pumped into the lower section of the absorption tower with a circulating pump, and a small part is sent to the steam-heated reconstruction tower for rebuilding, and the obtained lean liquid is sent to the upper section of the absorption tower for use. The carbon dioxide gas containing water vapor is obtained at the top of the regeneration tower and sent to the low-pressure flasher tank for use as a degassing material. [Natural gas desulfurizer]

2. The focus of technology use

(1) The ratio of lean liquid to semi-lean liquid

The ratio of lean liquid/semi-lean liquid is generally 1/3~1/6, which affects the partial pressure of carbon dioxide in the material. If the partial pressure of carbon dioxide is high, the ratio can be higher (such as 1/6), so that the heat energy consumption is reduced, and the temperature of the lean liquid is generally 55~70℃.

(2) Lean liquid and semi-lean liquid temperature

The semi-lean liquid is generally 70~80℃, the temperature of the inlet liquid is high, the heat energy consumption is low, but too high affects the temperature at the bottom of the absorption tower, which reduces the absorption power of the solvent. Instead, the heat consumption is added. For material gas conditions, there is a most suitable solvent temperature ratio. It can not only ensure the purity, but also give full play to its physical properties, so that its thermal energy consumption is reduced to a minimum.

(3) Carbon dioxide removal and consumption When the suction pressure is 2.7MPa, carbon dioxide can be removed to within 0.005, and the purity of carbon dioxide is within 0.1%. The key to the heat consumption is the partial pressure of carbon dioxide in the material gas. High partial pressure, low heat and energy consumption, generally during this period of thermal insulation removal of carbon dioxide. Under normal circumstances, there is no need to consume heat, but to maintain a stable absorption and analysis of the temperature, it depends on the thermal balance between the material gas, the pure gas and the regeneration gas. Generally, since the regeneration gas takes a lot of heat, it is necessary to supplement the heat (such as low-level energy such as hot water) to maintain the temperature.

(4) High pressure flash evaporator and purity of recovered carbon dioxide

The non-polar gases hydrogen, nitrogen, methanol, CH and other advanced hydrocarbon compounds in the MDEA solvent have low solubility, so the loss of pure gas is very small, but when the suction pressure is high, the carbon dioxide in the regeneration gas is less than 98% If the suction pressure is 2.7MPa, there is high pressure flash steam in the process to improve the purity of carbon dioxide. The pressure of the flash evaporator is selected according to the purity requirements. Generally, 96% of the carbon dioxide can be recovered, and its purity can reach 99.5. When the suction pressure is less than 1.8MPa, carbon dioxide with a purity higher than 98.5% can be obtained without using a high-pressure flash evaporator during the process.

(5) Solvent loss: Since MDEA reacts with carbon dioxide to form bicarbonate without forming nitroformate, it will not decompose. In addition, MDEA itself has a low partial pressure of steam (less than 0.01mmHg at 25°C), so the loss of MDEA is small,

3. Technical characteristics

(1) N-Methyldiethanolamine (MDEA) solvent has good stability, is not easy to decompose, and has no corrosive irritation to carbon steel.

(2) The partial pressure of steam of MDEA itself is low, and the volatility is also low.

(3) MDEA decarbonization technology can remove hydrogen sulfide and organic sulfur while absorbing carbon dioxide.

(4) It has relatively low solubility to non-polar gases H2 and N2 during the absorption process, so the loss of pure gas is also small. This feature further constitutes its bright future as a decarburization solvent.