JPS63312599A - Hot water heating type evaporator for liquefied natural gas - Google Patents

Abstract

PURPOSE:To supply vaporized LNG gas even at the time of service interruption by providing a hot-water holder holding a flow of hot water for required time in a pipeline between hot-water heater for heating and an evaporator. CONSTITUTION:A hot-water holder 5 is disposed between a hot-water heater 4 and an evaporator 1, the internal pressure thereof is increased to be substantially equal to the pressure in a connecting pipeline with nitrogen gas from a nitrogen gas bomb by a pressure controller 9, and the internal water level is kept at a designated position by a level controller 7. When the operation of a hot-water circulating pump 3 is stopped due to service interruption, hot water in the hot water holder 5 is pushed out by the internal pressure to flow in the evaporator 1, and heat of evaporization is supplied to low-temperature LNG similarly to the ordinary case, whereby hot water is let out of the evaporator 1 to be transferred to a hot-water receiver 2.

Description

[Detailed description of the invention] industrial application field) The present invention relates to a hot water heating type evaporator for liquefied natural gas.

Prior art) Liquefied natural gas (hereinafter referred to as LNG) has been widely used in recent years for large-scale demand such as electricity, city gas, and steel because its supply and price are stable and it is a clean energy with little pollution. It's been getting worse. Since LNG has already been refined locally at the production site, it can be used as city gas by evaporating it and adjusting its calorie content with LPG or air, so demand is increasing for city gas in small and medium-sized cities in rural areas. For the evaporation of LNG, a seawater heating method using seawater as a heat source is generally used for large-capacity products, and an air-heating evaporation method using air for small-capacity products. The air-heated evaporation method utilizes the heat contained in natural air, and requires less heat sources and other utilities. LNG is passed through the heat transfer tubes of the vertical tube group, and heat is transferred by generating natural convection of air on the outside of the tubes.As mentioned above, it is energy-saving and has the advantages of easy operation and maintenance. have. However, when the atmospheric temperature drops, such as during the winter, this air heating evaporation system cannot be used, and instead a hot water heating evaporator is installed separately and used. This hot water heating type evaporator uses a shell and tube type evaporator to heat low-temperature LNG with hot water and vaporize it.

Hot water for heating (pump, gas-fired or steam heating type heater, etc.) is connected via a pipe to form a hot water heating circulation line to supply hot water to the evaporator. However, the hot water heating type evaporation described above The device has the following problems to be solved.

Problems to be Solved by the Invention) In the above-mentioned LNG hot water heating type evaporator, hot water circulation is carried out by an electric pump, so when a power outage occurs, the pump stops driving and the hot water circulation also stops. If a city gas production factory does not have a large gas holder, it usually has its own in-house power generation equipment, and in the event of a power outage, this in-house power generation equipment is immediately activated for backup, but the rated output cannot be reached. A short-term power outage (usually within 1 minute) is unavoidable until this happens.During this time, hot water circulation stops, and in the evaporator, heat is taken away from the hot water side due to the latent heat of evaporation of the LNG, causing the temperature to drop. The temperature will drop below zero and it will freeze inside the heat transfer tube. It is not only difficult to thaw the ice once frozen inside the heat exchanger tubes, but also there is a risk of causing serious damage, including destruction of the evaporator. One way to solve this problem is to cut off the flow of low-temperature LNG into the evaporator in the event of a power outage, and immediately drain the water inside the evaporator to the outside by operating a valve, but it is difficult to operate the valve in an emergency, and the There are inconveniences such as the need to install a gas holder to compensate for interruptions in the supply of vaporized LNG gas.

Means for Solving the Problems) The present invention has been made to solve the problems of the conventional hot water hot water heating type evaporator for LNG as described above, and its gist is to evaporate liquefied natural gas using heated hot water. In an evaporator that evaporates water, a hot water holder is provided in the pipe between the hot water heater and the evaporator, which is pressurized to an appropriate pressure with gas such as nitrogen gas and holds the flow rate of hot water for the required time. This is a hot water heating type evaporation device for liquefied natural gas, and although it is a very simple device, the hot water does not freeze even during a power outage, and the vaporized LNG gas is not interrupted. A new L that can be supplied to
This is an NG hot water heating type evaporator.

The contents of the present invention will be further explained in detail based on the drawings. Fig. 1 is a flow system diagram showing one embodiment of the device according to the present invention. hot water is passed through each. 2 is a hot water receiver which receives hot water coming out of the evaporator 1 and also serves as a suction tank for the hot water circulation pump 3. Reference numeral 4 is a furnace-type hot water heater that burns fuel such as city gas to heat the circulating hot water to a required temperature, and the outlet temperature of the hot water is set to a predetermined temperature by adjusting the amount of fuel with a temperature indicator controller 6. controlled by. A steam heating heat exchanger may be used instead of a heating furnace.5
is a hot water holder, which is installed between the hot water heater 4 and the evaporator 1, and its internal pressure is increased by nitrogen gas from a nitrogen gas cylinder to approximately the same pressure as the connecting pipe using the pressure regulator 9, and its internal water level is It is maintained at a predetermined position by a liquid level controller 7. If pressurized air is available, this air may be used instead of nitrogen gas for pressurization, or other non-condensable gas may be used as long as it is insoluble in water. Alternatively, instead of pressurizing with gas, if there is a high structure, it may be used as a head tank system.

Function) The function of the present invention having the above configuration will be explained. The hot water extracted from the hot water receiver 2 is pressurized by the circulation pump 3, enters the hot water heater 4, is heated, is controlled to a predetermined temperature (generally around 80°C) by the temperature indicator controller 6, and leaves the hot water heater 4. hot water holder 5
The amount of hot water entering the hot water holder 5 is controlled by the control valve of the liquid level controller 7, and is substantially proportional to the flow rate of hot water leaving the hot water holder 5. The pressure inside the hot water holder 5 is constantly maintained at a predetermined pressure or higher by appropriately introducing nitrogen gas using a pressure regulator 9. The hot water in the hot water holder flows into the tube side of the evaporator L at this pressure, and the low temperature LN on the shell side flows.
After supplying the heat of evaporation to G, it returns to hot water receiver 2. The amount of hot water circulated is controlled to a required flow rate according to the load on the evaporator 1 by a flow rate indicating controller 8 installed in the pipe between the evaporator 1 and the hot water receiver 2. When the hot water circulation pump 3 stops operating due to a power outage, the hot water in the hot water holder 5 is pushed out by its internal pressure and flows into the evaporator 1, where it is converted into low-temperature LNG.
Heat of evaporation is supplied to the water in the same way as in normal times, and the water leaves the evaporator 1 and is transferred to the hot water receiver 2. The liquid level in the hot water holder 5 decreases as the hot water flows out, but since nitrogen gas is introduced by the pressure regulator 9, the internal pressure is maintained constant, so the amount of hot water flowing out is also constant. hot water holder 5
The retention capacity may be sufficient as long as it corresponds to the time it takes for the private power generation equipment to start up, and it is usually the capacity for about one minute. When the hot water circulation pump 3 is restarted by energization, the hot water in the hot water receiver gradually passes through the hot water heater 4 and then is transferred to the hot water holder 5. At this time, the nitrogen gas in the hot water holder 5 is released through the vent valve. You need to open it and pull it out. When the hot water level in the hot water holder 5 reaches a predetermined level, the vent valve is closed and the water is pressurized with nitrogen gas.

Effects of the Invention) According to the present invention having the above-described configuration and operation, hot water for heating can be flowed in the same way as in normal times even during a power outage, despite being a very simple device, so that generation of LNG gas can be prevented. The present invention is extremely useful industrially because it eliminates the problem of hot water freezing in the evaporator without interruption.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram showing an embodiment of the apparatus according to the present invention. 1: Evaporator, 2: Hot water register - ° bar, 3: Hot water circulation pump, 4: Hot water heater, 5: Hot water holder, L: L
NG liquid, G: LNG gas, F: Fuel, W: Make-up water.

Claims (1)

[Claims] In an evaporator that evaporates liquefied natural gas using heated hot water, the pipe between the hot water heater and the evaporator is pressurized to an appropriate pressure with gas such as nitrogen gas, and the amount of hot water for the required time is increased. A hot water heating type evaporator for liquefied natural gas, characterized in that it is equipped with a hot water holder having: