Energy saving potential of LNG cold energy utilization
LNG is a -162 liquid mixture at low temperature, which has been purified and liquefied by natural gas. The power and utility of each tonne of LNG produced is about 850 kWh. When LNG is vaporized at 1 atm pressure, approximately 230 kWh/t is released from -162 to 5 ℃. In actual operation, the LNG needs to be pumped to increase the pressure and then be blown out, some of the cold energy can be converted into pressure energy, and the cold energy - temperature load curve changes accordingly, as shown in figure 1. Under 5.5 MPa and 8 MPa, the cooling energy released by LNG can be 203 and 190 kWh/t respectively.
The value of cold energy at different temperature levels depends on the cooling efficiency at this temperature range. The lower the temperature, the higher the energy consumption. The LNG of -162 is gasified at 8 MPa, and the cold energy is 333 kWh/t when heating up to 5 ℃. A 3 million ton / year LNG receiving station can use cold power of 65 MW, equivalent to about 1 billion degrees of electric energy. If China consumed 3.2 billion m3/ year of natural gas in 2020, the imports and domestic LNG would add 60 billion m3/ year, nearly 50 million tons/year (slightly less than Japan's current imports). It can be used for 15 billion degrees in cold energy. That's equivalent to a 4 million kW power station.
Potential economic benefits of cold energy utilization in large-scale LNG plants
The cold energy utilization of the large LNG terminal has been completed so far, indicating that if the downstream market can be fully arranged, the cold energy of large scale LNG project could be utilized to a considerable extent. A 3 million 500 thousand ton / year LNG project is located in a large circular economy zone, with large scale, temperature distribution suitable for heavy chemical industry and other low-temperature cold energy users; The total cooling load is more than 70 MW, including the large-scale air separation, the separation of the associated light hydrocarbon of the oil field and the low temperature crushing, dry ice and cold storage of the cold media circulation system. More than 70% of the cold can be used. The feasibility study shows that the total economic benefit of the cold savings of the receiving station and the savings of SCV fuel gas income plus taxes is about 400 million yuan per year. An internal rate of return on investment is 15 per cent, five percentage points higher than the non-use of cold-energy projects. The cold energy downstream users can purchase LNG cold energy at a lower price than traditional electricity consumption. So they have a higher internal rate of return and they have an economic benefit of several hundred million yuan per year.
Economic benefits potential of cold energy utilization in small LNG projects
The initial planning of a small LNG satellite station in the county level will increase the cold energy utilization facilities project, the first phase 40,000 tons/year LNG scale; The cooling load is about 800 kW by cold - media circulating system to cold storage, indoor skating rink and air conditioning. The investment is about 10 million yuan, and the recycling period is 7 to 8 years.
In addition, the pressure of the main pipeline network is quite different from the pressure of the urban branch network. For example, the design pressure of the west gas east line is 12 MPa, while the operating pressure of the urban gas pipeline is generally 1.6 MPa. There is a pressure regulating facility at the gate of the connecting line. At present, most of these pressure can be wasted in the throttle valve, and the resulting temperature drop often causes failure. With the technology of shock cooling and expansion, these valuable pressure can be recycled and converted into cold energy. These cold energy can be used directly, and can also be used to liquefy (more than 10%) of pipeline gas liquefaction, which is used to adjust peak. This is also a cold energy resource. Optimized design of large or small LNG projects can achieve better investment efficiency.