The control equipment for the integrated use of cold energy in LNG vessels

The design of control equipment for the cold energy recovery and utilization of LNG ships is the focus of ship technology and a prerequisite for equipment manufacture. By analyzing the design background and design status of LNG ship cold energy recycling control equipment, the study forms design ideas and prepares equipment materials. It optimizes design methods and compares and evaluates them with traditional control equipment. After a series of evaluation tests, it is found that the LNG ship cold energy comprehensive utilization control equipment can effectively achieve the purpose of energy saving and emission reduction and solve the problems of high operating costs and environmental pollution of traditional LNG ships.


Introduction
The LNG ship cold energy intelligent recycling technology recovers part of the cold energy in LNG to cool down the refrigerated tank without the need for additional mechanical refrigeration equipment, reducing the cost of refrigeration.The intelligent recycling of cold energy achieves energy saving and emission reduction compared to the direct discharge of cold energy, making fuller use of resources.Therefore, the application of the substantial cold energy recovered from LNG cold energy to ships will become a trend for future development.Through the research of LNG ships' cold energy comprehensive utilization control equipment, we actively respond to the national call for energy conservation, which is an important help to promote the green development of energy conservation and emission reduction in the ship transportation industry and contribute to the construction of domestic first-class inland waterway shipping.

Overview of LNG ship cold energy recovery and control equipment technology
With the adjustment of China's energy structure, the use of LNG has also increased rapidly, and the construction of LNG receiving terminals has flourished.the design of LNG storage equipment plays a vital role in the energy industry.Countries around the world attach great importance to the design and manufacture of LNG energy storage tank equipment. [1]The storage and transportation equipment developed for LNG applications in China still has gaps with international storage and transportation equipment and so on.In the research of LNG storage and transportation equipment, the focus should be on the research of LNG storage tank insulation technology, the optimization design of LNG storage containers, and the research of low-temperature heat exchanger performance.

Design architecture for control equipment for cold energy recovery from LNG vessels
A lightweight design is chosen for the design of cold energy recycling control equipment for LNG ships.The lightweight design of the austenitic stainless steel deep-cooling vessel is conducive to the adjustment of the permissible strength of the material, the regulation of the performance of high-strength steel, and the development of a new structural design to ensure durability and reliability.The design architecture of the LNG ship cold energy recycling control equipment is shown in Fig. 1.

Reduced pressure gasification valves Booster valves
Fig. 1 Design architecture of control equipment for cold energy recovery on LNG vessels The booster of the LNG gasifier in Fig. 1 works by increasing the volume of the gas with no change in space, then the pressure naturally becomes greater.Once the LNG enters the booster, the booster absorbs the heat from the wandering air, thus increasing the volume of the liquid gas in the booster.This causes the liquid to gasify to a gaseous state before it is returned to the storage tank, where the pressure is then increased.The BOG storage tank, on the other hand, is equipped with a BOG pressure-reducing valve in the gas phase piping of the LNG storage tank in order to prevent the pressure inside the tank from rising due to heat leakage. [2]When the pressure inside the LNG storage tank rises to a set value, the pressure-reducing valve opens slowly and releases the gas inside the LNG storage tank.When the pressure drops back below the set value, the pressure-reducing valve closes automatically. [4]

LNG ship cold energy recovery and utilization control equipment technology route
The research and development of the LNG ship cold energy recovery process is mainly the design and calculation technology of power equipment and storage and transportation equipment.It provides great help to the design and operation of the main equipment involved in the key links of LNG liquefaction, LNG storage and transportation, LNG receiving, and LNG vaporization.It promotes the standardization and high quantification of LNG series equipment and system process technology. [5]The technical route of the LNG ship's cold energy recovery and utilization control equipment is shown in Fig. 2. In the LNG storage system, a self-pressurizing vaporizer disposes of the excess evaporated gas in the LNG storage tank.It maintains a stable pressure in the LNG storage tank without explosion due to excessive pressure in the storage tank.The BOG system is processed in the following way: the LNG cold energy evaporated gas is returned to the storage tank, and the LNG cold energy evaporated gas is transferred to the condenser and condensed.The evaporated gas then goes to the pipeline and is discharged through the tank pressure safety valve.

Hardware components of the LNG ship's cold energy recovery and utilization control equipment
Traditional LNG ship equipment often uses large and heavy-pressure vessels.The choice of pressure vessel lighting can solve current technical bottlenecks and achieve energy and material savings.The design of LNG control equipment includes 12 categories of low-temperature valves, such as LNG butterfly valves, ball valves, gate valves, globe valves, pressure-reducing valves, throttling valves, safety valves, check valves, needle valves, breathing valves, temperature control valves, and air evacuation valves.valves.These 12 categories of cryogenic valves can effectively control the temperature of the LNG and ensure that the LNG can be delivered and used effectively and efficiently.The design of the 12 major types of process control valves involved is a key aspect of LNG liquefaction, storage, and transportation. [6]

Intelligent control of cold energy recycling control equipment for LNG vessels
The heat exchanger adopts a two-stage heat exchange method, using coolant for intermediate transition, so that the low-temperature cold energy released by LNG can be transferred to the room temperature medium of cooling water.After a series of heat exchange transformations, the LNG can be transformed into cold energy to be stored in the cold energy recovery storage tank. [7]The intelligent control of the LNG ship cold energy recovery and utilization control equipment is shown in Fig. 3. LNG ship cold energy uses intelligent component control equipment processes.After entering the energy recovery storage tank, it enters the multiple electronic control valves according to the amount of LNG cold energy in the storage tank to control the storage tank.After the transmission of LNG cold energy pressure to the pressure sensor, the pressure sensors use multiple devices to transmit information.[3]   They are temperature and humidity sensors.The information collected by the two sensors is encoded in an encoder and compiled for transmission to a memory module with LED LCD and a communication module, where it is analyzed in the power controller microcontroller control module.

LNG ship cold energy recovery and utilization control equipment applicability simulation test
The main components of LNG cold energy recovery are also the different heat exchangers.The degree of cold energy recovery from LNG ships is further introduced through simulation tests of the heat exchangers.The heat exchangers are modeled, and data analysis is carried out.A multi-node parametric model of the heat exchanger is thus established using a recursive calculation method that divides the heat exchanger piping into corresponding small modular micro-element segments.The exit of each micro-element segment serves as the inlet of the next micro-element segment for a specific parameter.After a specific calculation method, the variation of the corresponding parameter under specific conditions is obtained.When selecting the micro-element control body, the x-direction will be selected for the longitudinal direction of the heat exchanger.^x is determined by the diameter of the heat exchanger.The y-direction is the direction of the fluid.^y is determined by the number of microelements selected. [8]A schematic of the heat exchanger computational micro-element control body is shown below in Figure 4 Figure 4 Schematic diagram of the heat exchanger computational micro-element control body The heat exchanger formula is shown below. [9]ontinuity equation: m=ʌ\4d²pv Energy equation: cpim1(t1-ti+1) =cpim2(tj+1-tj) In order to compare the data, the actual measurements of the temperature at the inlet and outlet of the glycol in the air cooler and the outlet temperature of the air with the flow rate of the glycol are shown in Figs. 5 and 6.In terms of its simulation, the model of the steady-state distribution parameters of the air cooler agrees with the experimental results, indicating that the parameter variations have very good experimental values and are forward-looking.
At present, domestic LNG cold energy recovery is mostly applied to cold energy generation, maintaining cold storage temperature, desalination, and air separation.LNG ships are placed in a specific test environment to test the realization rate of LNG ship cold energy recovery control equipment. [10]Through the applicability test of the LNG ship cold energy recovery and utilisation control equipment, the results were obtained as shown in Through LNG ship cold energy recycling control equipment applicability test, desalination device, air separation device, cold storage, and air conditioning, the engine for LNG ship cold energy recycling realization rate is high.The LNG ship cold energy comprehensive utilization control equipment has considerable prospects.

Concluding remarks
The LNG ship cold energy intelligent recycling technology follows the development trend of national new energy.The design of LNG ship cold energy comprehensive utilization control equipment is forward-looking.It has advanced and unique characteristics.The use of LNG ship cold energy recycling technology can make fuller use of LNG ship cold energy resources.Therefore, the application of the huge energy recovered from LNG cold energy to ships has become a trend for future development, and the intelligent recycling of cold energy from LNG ships will definitely take a huge advantage in the future.

Fig. 2
Fig. 2 Technical route for LNG ships' cold energy recovery and utilization control equipment LNGIn the LNG storage system, a self-pressurizing vaporizer disposes of the excess evaporated gas in the LNG storage tank.It maintains a stable pressure in the LNG storage tank without explosion due to excessive pressure in the storage tank.The BOG system is processed in the following way: the LNG cold energy evaporated gas is returned to the storage tank, and the LNG cold energy evaporated gas is transferred to the condenser and condensed.The evaporated gas then goes to the pipeline and is discharged through the tank pressure safety valve.

Fig. 3
Fig. 3 Intelligent control of cold energy recovery control equipment for LNG vessels

Fig. 5
Fig. 5 Plot of experimental results of glycol inlet and outlet and air outlet temperatures as a function of glycol flow rate

Table 1 Table 1 .
Applicability testing of cold energy recovery control equipment for LNG vessels