JPH0419424B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a hot water heating type evaporator for liquefied natural gas.

Conventional technology 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 coming. Since LNG has already been refined locally at its production site, it can be used as city gas as is by evaporating it and adjusting its calorie content with LPG or air, so demand for it as city gas in small and medium-sized cities in rural areas is increasing. 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-temperature evaporation method utilizes the heat possessed by natural air, and is the most energy-saving method because it requires less heat source and other utilities. In this method, LNG is passed through a group of vertical tubes with fins made of aluminum alloy, etc., and heat is transferred by generating natural convection of air on the outside of the tubes. It has advantages such as easy operation and maintenance. 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 achieve low temperature.
LNG is heated with hot water and vaporized.
Hot water for heating is supplied to the evaporator by connecting a pump, gas-fired or steam heating type heater, etc. with a pipe to form a hot water heating circulation line. However, the hot water heating type evaporator described above has the following problems that must be solved.

Problems to be Solved by the Invention In the LNG hot water heating type evaporator as described above, hot water circulation is dependent on an electric pump, so in the event of a power outage, the pump will stop driving and the hot water circulation will also stop. . If a city gas production factory does not have a large gas holder, it usually has its own in-house power generation equipment, and when there is a power outage, the in-house power generation equipment is immediately activated and backed up, but the rated output cannot be reached. A short power outage (usually less than 1 minute) is unavoidable until this happens. During this time, hot water circulation stops, and in the evaporator, the latent heat of vaporization of the LNG steals heat from the hot water side, causing the temperature to drop below zero and 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 heating type evaporator for LNG as described above, and its gist is to After the hot water is sent to a hot water heater by a circulation pump and heated to a predetermined temperature, the hot water is supplied to an evaporator and used for evaporation of liquefied natural gas, and then the hot water is returned to a hot water receiver for circulation. The type evaporator is characterized by being equipped with a hot water holder in the pipe line between the hot water heater and the evaporator, which is pressurized to an appropriate pressure with gas such as nitrogen gas and holds a hot water flow rate for the required time. This is a hot water heating type evaporation device for liquefied natural gas.Although it is a very simple device, it can supply vaporized LNG gas without freezing hot water even during a power outage, and without interrupting the supply of vaporized LNG gas. This is a new LNG hot water heating type evaporation device. The contents of the present invention will be further explained in detail based on the drawings. FIG. 1 is a flow diagram showing an embodiment of the apparatus according to the present invention. In the diagram, 1 is the Ciel & Tube type.
This is an LNG evaporator, with LNG flowing through the shell side and hot water for heating through the tube side. A hot water receiver 2 receives the 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 the heating furnace. Reference numeral 5 denotes a hot water holder, which is installed between the hot water heater 4 and the evaporator 1, and whose internal pressure is increased by nitrogen gas from a nitrogen gas cylinder to approximately the same pressure as the connecting pipe using a pressure regulator 9. The water level 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. 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 exits the hot water heater 4. Next, 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 1 at this pressure and returns to the hot water receiver 2 after supplying the heat of evaporation to the low temperature LNG on the shell side. 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 indicator controller 8 installed in a 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, flows into the evaporator 1, supplies heat of vaporization to the low-temperature LNG, and exits the evaporator 1 as in normal times. and 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 restarts due to energization, the hot water in the hot water receiver gradually passes through the hot water heater 4 and is transferred to the hot water holder 5, but at this time, the nitrogen gas in the hot water holder 5 is released by opening the vent valve. You need to take 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 structure and operation, hot water for heating can be flowed in the same manner as in normal times even during a power outage, despite the extremely simple device.
The present invention is extremely useful industrially because it can eliminate the problem of freezing hot water in the evaporator without interrupting the generation of LNG gas.

[Brief explanation of drawings]

FIG. 1 is a flow diagram showing an embodiment of the apparatus according to the present invention. 1...Evaporator, 2...Hot water receiver, 3...Hot water circulation pump, 4...Hot water heater, 5...Hot water holder, L...LNG liquid, G...LNG gas, F...Fuel, W
...Supplementary water.

Claims (1)

[Claims] 1. After sending the hot water derived from the hot water receiver 2 to the hot water heater 4 by the circulation pump 3 and heating it to a predetermined temperature, the hot water is supplied to the evaporator 1 and used for evaporation of liquefied natural gas, and then the hot water is converted into hot water. In a hot water heating type evaporator for liquefied natural gas that is returned to the receiver 2 for circulation, a hot water heater 4 and an evaporator 1 are installed.
A hot water heating type evaporator for liquefied natural gas, comprising a hot water holder 5 which is pressurized to an appropriate pressure with a gas such as nitrogen gas and holds an amount of hot water for a necessary time in a pipe line between the liquefied natural gas and the like.