Coal chemical membrane separation technology

Remove catalyst ultrafine powder and emulsified oil from rapid cooling water and washing water

Ceramic membranes are applied in the field of coal chemical oil-water separation, which can separate emulsified oil and ultrafine catalyst particles in water. The removal rate of emulsified oil is over 90%, and the removal rate of catalyst is as high as 99%; Can effectively solve the blockage problem of water washing tower and heat exchanger, ensuring stable operation of the device; Save investment and land occupation, with a simple process and easy operation, suitable for technical transformation of coal chemical projects.

1、 Process background

The methanol to olefin (MTO) unit is the key unit of the coal to olefin project. In the actual production process, the MTO product gas still contains a small amount of catalyst fine powder and oil substances after passing through the three-stage cyclone separator, and it condenses and accumulates in the subsequent water system. The emulsification forms sludge and lotion, which speeds up the blockage of tower trays, heat exchangers, air coolers and other equipment in the water system, and also makes the separation of recycled water more difficult, significantly increasing the energy consumption of the unit.

Anhui Shengchuan has developed ceramic membrane separation technology to purify the emulsified oil and catalyst in the rapid cooling water and washing water of MTO process, solving the problem of equipment blockage caused by emulsified oil and catalyst in the water system.

2、 Process characteristics

(1) High separation accuracy and thorough removal of impurities. The ceramic membrane has a separation accuracy of up to 50nm, which can completely remove catalyst ultrafine powder and emulsified oil from quenched water and washed water, with a separation efficiency of over 99%.

(2) No need to add chemical agents. Urgent cold water and washing water can directly enter the ceramic membrane separator for treatment, without the need to add coagulants or demulsifiers, saving chemical costs.

(3) The process flow is simple. The ceramic membrane separation system does not require complex pretreatment, has a simple process, high system integration, and is easy to operate.

3、 Process Overview

This process adopts ceramic ultrafiltration membrane cross flow filtration technology to remove catalyst and emulsified oil impurities from quenched water and washed water. The rapid cooling water and washing water are pumped into the ceramic membrane filter. The catalyst ultrafine powder and emulsified oil are trapped in the concentrated liquid by the ceramic membrane, while the purified water is filtered and infiltrated into the system through the ceramic membrane for continued use. Ceramic membrane filtration has high precision and good water quality, completely solving the impact of impurities in quench water and washing water on MTO water system equipment, avoiding blockage of trays, heat exchangers, and air coolers, significantly extending equipment operation time, improving system stability, and reducing energy consumption.

4、 Technical advantages

(1) Water production advantage. Due to the small particle size of the catalyst, with 80% below 10 μ m, conventional cyclone separators have poor separation efficiency. Even high-efficiency micro cyclone separators have a separation efficiency of no more than 90%, and the catalyst content in the produced water is about 30mg/L. The ceramic membrane has a separation accuracy of up to 50nm, with a separation efficiency of over 99% for catalyst granules and emulsified oil particles, and a water production catalyst and emulsified oil content of less than 5mg/L.

(2) Cost advantage. Taking the MTO unit of a coal chemical enterprise in Baotou as an example, after entering the commercial operation stage in 2011. the unit needs to be cleaned three times a week due to heat exchanger blockage during production and operation. The cleaning cost for each unit is about 20000 yuan, and the annual cleaning cost is about 3 million yuan; The main washing tower tray is blocked, and partial shutdown washing treatment is carried out. During this period, the product gas is released into the flare, and methanol consumption exceeds 3 million yuan; Using xylene injection to solve the problem of tray blockage, the annual consumption of xylene exceeds 1 million yuan; Due to system congestion, energy consumption has significantly increased. If ceramic membrane separation technology is adopted to solve the problem of catalyst and emulsified oil carryover in rapid cooling water and washing water, the annual operating cost can be saved by more than 7 million yuan.

(3) Energy saving and environmental protection advantages. To solve the problem of MTO water system blockage, some companies are considering using compressor turbine condensate instead of purified water, but this will lead to waste of purified water resources and increase the discharge of sewage. If ceramic membrane separation technology is used, there is no need to change the water system design, and the purified water quality can be directly improved, reducing the discharge of sewage. Moreover, by avoiding the injection of xylene into the system, the COD discharge of sewage can be reduced.