SU838273A1 - Method of preparing natural gas - Google Patents

Description

(54) METHOD FOR PREPARING NATURAL GAS

one

The invention relates to a technique for the treatment of evaporated natural gas, and can be used in gas supply systems for combustion in main engines of methane-carrying vessels, as well as in other installations transporting liquefied natural gas whose heat engines use gas.

On modern vessels transporting liquefied gases, part of the cargo (about 0.25% daily) is evaporated. To prevent pressure in the cargo tanks, the gaseous part of the cargo must be removed from them. Simple combustion of gas. In special installations and the discharge of combustion products into the atmosphere is very uneconomical, and therefore the vaporized gas can be either re-liquefied and returned to cargo tanks, or used as fuel for main engines.

There are facilities for processing the vaporized part of the cargo in which the gas is divided into two streams — one is used as fuel for the main engines, and is subjected to re-liquefaction and is returned to the cargo tanks. By virtue

their is that the loss of cargo due to re-liquefaction of gas and its return to cargo tanks II is partially replenished.

However, to ensure re-liquefaction of gas, large electrical energy costs are needed, therefore, with the existing price ratios for liquid fuel and gas, the schemes with re-liquefaction of gas (methane) are not economical.

f

There is a known method of preparing natural gas, according to which all the evaporated gas is used as fuel for main engines. At the same time, the vaporized gas is compressed in the compressor to the pressure required by the consumer, the main engine, followed by 1 W 1 M heated-compressed gas to the temperature from which it is fed to the combustion. The heating of the gas is realized in heat exchangers using fresh steam 2.

Claims (2)

The disadvantages of this method are as follows. The monosity, the diffusion of the process is compressed, significant and associated with the capacity of the ship power station (for example, for a methane leverage of 125 thousand meters, the required compression power of the gas is about 200 700 kW). To heat the gas, various heat transfer media (steam and antifreeze) are needed. which makes it difficult to maintain installations. The purpose of the invention is to reduce energy consumption in the preparation of evaporated gas for use as fuel for power plants. The goal is achieved by the fact that the gas is compressed to a pressure Determined by the formula (P3 / d) where p is the pressure of the vaporized gas; P2 is the gas pressure at the end of compression; RZ - gas pressure at the entrance to the installation; heated to ISOISO C and expanded in a turbo delta located on the same shaft as the compressor. FIG. 1 is depicted, respectively, in T-S units, the installation cycle operating according to the proposed method; in fig. 2 - basic installation diagram. The gas evaporated in cargo tanks at a pressure pi (close to atmospheric) compresses in the process 1-2 to a pressure p2, exceeding the lowest pressure p3 at the gas inlet to the main engine (Fig. 1). Then the gas is heated in the process of 2-3 with its isobaric heat exchange with seawater and waste steam. After preheating, the gas is expanded, with work done in process 3-4. up to the required pressures rz and temperature Tz, withdrawing at this time the expander for use in the process of compression 1-2. Since the temperature of the gas before expansion is higher than the temperature T at the end of the compression process, the work of expansion of the gas is greater than that of its compression. Thus, the proposed method of gas preparation does not require a constant supply of work from shipboard electrical installations. After expansion, the gas with parameters rzTz enters for combustion in the main engine of the ship power plant. In this calculation, the magnitude of the gas pressure P2, the higher the pressure p3 at the entrance to the main engine, is carried out according to (P3 / ft). The gas evaporated in the cargo tanks 1 flows to the gas compressor 2, where it is compressed to a pressure p2 exceeding the pressure p3. in the seawater preheater 3 and in the preheater 4 the exhaust gas is sent to expander 5, where, the gas expands, it does the work that is used to drive compressor 2. After the expander, gas with pressure p3 and temperature Tc 293-303 K is directed to fuel quality to top or boat engines, steam generators. The device is brought into operation by a small-sized starting device 6. The estimated annual economic effect from using the proposed method of preparing natural gas for its combustion in ship power plants is about 18 thousand rubles. for one transport unit. At the same time, the cost of installation using cargo as fuel is not significantly different from conventional fuel supply systems to main engines. Formula of the Invention A method for preparing natural gas during its transportation for use as a fuel for a power plant, including compression in a gas compressor evaporated during transportation , its subsequent heating, and combustion in the installation, characterized in that, in order to reduce energy consumption, the gas is compressed to a pressure determined by the formula P2 P () - where p is the pressure evaporation of gas; p is the gas pressure at the end of compression; P, is the gas pressure at the unit inlet; heated to a temperature of 150-180 ° C and expanded in a turbo unit located on the same shaft as the compressor. Sources of information taken into account in the examination 1.Patent of France No. 2189678, cl. F 17 C 13/00, 1970. 2. Schiffe und Hafen, 1971, 23, N “5, C.391-396. f) cansi To the tabnon dbig thea OmpaSatnaHHtiu steam