Solutions for condensation recovery and steam balancing systems for methanol storage tanks in the coal chemical industry

chemical industry refers to the process of converting coal into gases, liquids and solid fuels and chemicals by chemical processing. The chemical industry "> coal chemical industry is mainly distributed in coal-producing areas, traditional coal chemical industry involves coke, electric stone, synthetic ammonia and other fields, the new coal chemical usually refers to coal oil, coal methanol, coal dimethyl ether, coal olefins, coal glycol and so on.now we mainly share the VOCs of methanol storage tanks in the coal methanol section. Mainly consists of two parts:
1) tank pipeline and in addition to the breathing valve dynamic sealing point, mainly contains the tank attached static sealing point and the mechanical seal of the pump connected to the tank as the representative of the dynamic sealing point, these points need to establish an LDAR system to control the process emissions of unorthorged VOCs. This part of the workload is small, and the coal methanol other sections such as low methanol washing, methanol distillation and other work sections implemented together, a set of device sealing points roughly in the thousands of points level (specific analysis).2) The second block is the main content of this paper, focusing on how to control the size of the methanol tank breathing and the loading system connected to the tank, the two parts of VOCs. Washing and activated carbon or other basic processes can meet the standards, and its one-time investment, operating costs relative to how to need enterprises to carefully consider the choice, and the storage tank discharge of methanol exhaust into the enterprise's internal boiler system its safety should be carefully assessed, corresponding to the design institute in the issuance of drawings should be more equipment safety assurance measures, and recommend communication with the local Safety Supervision Bureau to confirm.BI, methanol storage tank and loading basic situation
need to collect the type of enterprise methanol storage tank, flow and other basic data, the inner floating top of the methanol tank (in fact, most of the floating top) need to face the tank top transformation, specific specifications Can refer to the "petrochemical storage and transportation area VOCs management project oil and gas Unicom process implementation program and safety measures guidance" (need to read the full text of the site's historical article) issued in the 127 letter of technical requirements, emission standards can refer to GB31571 or local landmarks. This step determines the amount of condensation recovery equipment treatment and steam balancing system design.3. Condensation recovery pipeline and steam balance system design
VOCs treatment of methanol tank area is mainly for the oil storage and transportation tank area in accordance with the relevant norms or regulations need to be treated for the tank unorthomic discharge of tank top oil and gas centralized collection and management. The implementation method is to install a closed gas phase line at the top of the tank tank, to collect the methanol gas exhaled and transport it to the methanol gas condensation recovery treatment equipment designed and manufactured in accordance with the discharge flow, to recover the methanol gas discharged, to treat the exhaust emissions of the equipment, the emission limit is methanol gas <50mg/Nm3; The concentration of non-methane total hydrocarbon < 100mg/Nm3. Processing efficiency can be greater than 97%.For methanol gas emitted by tankers at the time of loading, VOCs emissions from the loading process are used in accordance with letter No. 127 and in accordance with the national standard "Volatile Organic Organics Unwed Emission Control Standard" (draft for comments), using "vapor balance" The system provides for "an air-connected system between the loading facility and the tank, which collects the vapor generated by the loading operation and returns it to the starting tank or other tanks connected to the steam space in the feed tank to achieve a balance with the volume of the material." "The method.4, methanol condensation temperature calculation confirmed
methanol related physical and chemical properties are sorted as follows:
according to the Antoine equation, accounting for the concentration of methanol saturated steam at different condensation temperature, to determine the condensation key temperature.
the calculation, the temperature can be between -70 degrees C and -80 degrees C, the latter is recommended, at this time the saturation steam concentration is 35 mg.
, condensation recovery process flow chart
According to the calculation of methanol vapor at different temperature conditions saturated vapor pressure and concentration table, methanol vapor at -80 degrees C residual concentration of 35mg/m3. Therefore, the project condensation unit is set to 3 degrees C, -35 degrees C, -80 degrees C three-stage condensation temperature, the basic flow can be seen in the following figure:condensation unit set segment condensation heat exchanger, by the pre-stage, the first level of shallow cold level, the second level of medium-cold level and the third level of deep cooling level. The front stage exchanges the residual air cooling after the 3rd deep cold stage condensation with the normal temperature oil and gas entering the oil and gas recovery treatment device, which reduces the oil and gas by about 5 to 10 degrees C. The first level of shallow cold, the oil and gas temperature from the ambient temperature to about 3 degrees C, the second level of medium-cold level, from about 3 degrees C to -35 degrees C, the third level of deep cold level, from -35 degrees C to -80 degrees C, so that 97% of methanol condensation liquefacation. After the rich adsorption unit (slightly), even if the operating conditions fluctuate can fully guarantee the emission of the standard. Technical indicators and configurations need to be determined in accordance with specific projects.6, control system process description
1) methanol tank feed when the discharge of methanol gas, after taking over the breathing valve exhalation direction of the pipeline, when the line pressure transmitter induction to 100Pa, automatically open the closed gas phase pipeline exhaust direction of the valve, storage tank discharge methanol gas to the recovery equipment, condensation recovery treatment;2) Steam balance system for methanol emissions from tanker vehicle loading, when the tanker vehicle is filled with armored alcohol, liquid methanol in the tank is pumped through the loading pump, transported to the loading crane pipe, the level of fluid in the tank is reduced, and the storage tank space pressure appears. Negative pressure value, when the line pressure transmitter sensed -100Pa pressure, automatically open the closed gas phase line suction direction of the valve, the tanker exhaust methanol gas along the suction line back to the storage tank, to achieve steam balance, while achieving zero emissions;3) The operation process of the condensation unit of methanol gas recovery equipment: methanol gas output from the closed gas phase line, transmission and recovery treatment equipment front end, pressure differential sensor induction to line pressure 100pa, start the fan, methanol gas in turn into the condensation unit first, second, third stage condenser, segmented condensation liquefaction, residual gas standard into the rich set (adsorption) unit;4) The operation of the methanol gas recovery equipment abunding unit: Methanol gas emitted by the tank system at rest is increased with the temperature. Methanol gas emitted by the volume expansion of liquid gas in the tank, at this time the recovery equipment is not in operation, methanol gas through the condensation unit channel, directly into the adsorption bed of the concentration unit, methanol parts are adsorbed by adsorbent, air standard;5) The overall energy consumption of the recycling device is low, the vast majority of electricity consumption, because the coal chemical methanol storage tank is small, the processing capacity is small electricity consumption is small, compared to washing and activated carbon and other traditional processes once investment and operation economy has more advantages, and safety assurance.
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