Use of liquefied natural gas

(4) Zhongyuan Oil Field liquefied natural gas plant

Zhongyuan Oilfield has built the largest LNG plant in China, with a raw gas scale of 26.65×104m3/d, a liquefaction capacity of 10×104m3/d, a storage capacity of 1200m3 and a liquefaction rate of 37.5%. At present, on the basis of fully absorbing foreign advanced technology, combined with the situation of relevant equipment at home and abroad, mainly for the characteristics of their own gas source, and research LNG process technology. The process adopts the common molecular sieve adsorption method for dehydration, and the liquefaction process uses propane precooling + ethylene precooling + throttling.

When the raw gas volume is 30×104m3/d, the yield is as high as 51.4% and the energy consumption is 0.13Kwh/Nm3. Its advantage is that each refrigeration system is relatively independent, reliability, flexibility. However, the process is relatively complex, requiring two kinds of refrigeration media and circulation, and the equipment investment is high. The liquefaction cost is low because the plant makes full use of the pressure energy of natural gas in oil field gas Wells.

(5) Small liquefied natural gas unit of Tianjin University

Compared with large LNG plants, small LNG plants not only have raw material advantages, market advantages, but also have low investment, relocation and flexibility. LNG plant mainly uses amine solvent system to pretreat natural gas and remove CO2 and other impurities; Molecular sieve dehydration; Liquefy several steps. The device adopts a single-stage mixed refrigeration system; Compressors for closed loop refrigeration cycles compress refrigerant. The single-stage refrigerant mixing process is simple and efficient, and is suitable for small LNG plants.

The compressor can be driven by gas turbines or electric motors. Where electricity prices are low, priority can be given to electric motors (low cost, simple maintenance). In areas where fuel gas prices are low, gas turbines will be a better option. The economic evaluation results show that the investment cost of liquefaction plants with gas turbine drives is 2 million to 4 million US dollars higher than that of electric motors. According to the cost estimation of a set of 15×106ft3/d liquefaction unit, the storage tank volume of the LNG project for peaking is 100,000 m3, while the LNG project for vehicle fuel only needs 700m3 storage tank, resulting in the final cost of LNG for peaking is 2.03~2.11 USD /1000ft3. However, the cost of automotive LNG is only 0.98~0.99 USD /1000ft3 [8].

(6) New liquefaction technology of Southwest Petroleum University

The process processes 3.0×104m3 of natural gas per day, which is mainly composed of raw gas (CH4:95.28%, CO2:2.9%) deCO2, dehydration, propane precooling, gas wave refrigerator refrigeration and cyclic compression systems. Using SRK equation of state as the basic model, natural gas liquefaction process software was developed. Natural gas compressor is powered by natural gas engine, and small load electric equipment is powered by natural gas generator set, which solves the problem of no electricity or power shortage in remote areas. Since there is no gathering pipeline available in remote areas, the unliquefied natural gas is cycled and compressed to improve the liquefaction rate of the whole unit.

CO2 was removed by the ethanolamine process (MK-4). Due to the small processing capacity, the absorption tower and the regeneration tower of carbon dioxide removal should use high-efficiency packing tower. Due to the mixed refrigerant, there is no mature technology and experience in design and operation management in China, and the instrument control system is more complex. At the same time, considering the high methane content in the raw gas, the pressure energy can be used. Therefore, natural gas direct expansion refrigeration is used as a natural gas liquefaction cycle process. Gas wave refrigeration belongs to isentropic expansion process. The gas wave refrigeration machine is developed on the basis of the hot separator and the theory of gas wave motion. It absorbs some advantages of the thermal separator in structure, and increases the key device of the microwave absorption cavity, which is obviously different from the thermal separator in principle, and makes more effective use of the pressure of the gas, and improves the refrigeration efficiency.

(7) Harbin Gas Engineering Design and Research Institute and Harbin Institute of Technology

The LNG system mainly includes natural gas pretreatment, low temperature liquefaction of natural gas, low temperature storage of natural gas and gas gasification and output. The treated natural gas is liquefied through a multi-stage mono-mixture condensation process, and the refrigeration compressor is powered by a natural gas engine. The LNG storage tank is a bimetallic walled insulated tank, the inner tank and the outer tank are made of nickel steel and carbon steel respectively.

Circulating gas compressors are generally driven by natural gas, which can save operating costs and make the investment quickly recovered. Compressors generally use non-lubricated special design to avoid natural gas being contaminated by lubricating oil. The turbine is equipped with an electronic speed control system, and the final blades of the new turbine are made of drill alloy, which improves the mechanical operation. The new clutch installed on the turbine compressor is flexible, they are relatively reliable, and can also adjust the clearance.