The installation position of LNG low temperature storage tank (low temperature tank) detector should be determined by combining the velocity and direction of air flow with the relative position and ventilation condition of potential leakage source, and easy for maintenance and calibration. The detector and the alarm controller should be installed in the way of minimum vibration. If the electromagnetic interference is likely to occur nearby, the armored cable or cable and metal sheath shall be used. The mounting height of the gas detector shall be determined according to the density of the combustible gas. When the gas density is greater than 0.97kg/m3 (standard state), the installation height is 0.3-0.6m away from the ground; when the gas density is less than or equal to 0.97kg/m3 (standard state), the installation height is 0.5-1.0m away from the top.

The following points should be followed in the layout and setting of the detector:

(1) the first to identify the cryogenic storage tank to be monitored, which may leak, leakage pressure, and calculate the unit time possible leakage and leak their direction, draw the checkerboard shaped distribution map, and divided into A, B, C3 grades according to the severity of speculation.

(2) the rise of air circulation, the dominant wind direction may according to the location and the phenomenon of air flow, air flow and natural habits and other channels, comprehensive speculation when there is substantial leakage, gas in the plane of the natural diffusion trend chart.

(3) according to the density of leakage gas (greater than air or less than air) and the upward trend of air flow, the three-dimensional flow trend diagram of leakage flow is finally synthesized.

(4) according to the monitoring range of three-dimensional flow concept of gas leakage, can make the initial point in the downstream position of the flow of the program.

(5) the point leakage state of the leakage point may be micro leakage or jet like leakage. If the micro leakage, then set up the position to close the leak, if the spray leakage is slightly away from the leak. The combination of these conditions, to set up the final scheme. So, to purchase the number and variety of detector can be estimated from the consideration of the final game in the trellis.

(6) for a large and medium-sized cryogenic storage tank with combustible gas leakage, it is suggested that there are 1 testing points at each distance of 10-20m.

(7) the detector should be installed below the bottom of the leak point to detect the gas whose density is greater than the air, and pay attention to the surrounding environment. For example, to the accumulation of combustible gas geosyncline trench, ditch in the underground cable field to the control room, a sealing cover of sewage trench, are often in the production or abnormal situation to the accumulation of gas places.

2, monitoring system architecture design

Low temperature Petrochemical liquefied natural gas (low temperature) structure and fire fire monitoring linkage control system take into account the different technological requirements of monitoring parameters of DC4-20mA transmission and transmission parameters of fire and fire extinguishing equipment, signal output linkage control requirements. Monitoring of process parameters based on the conversion of data communication protocol, the design structure of explosion-proof type DDZ converter, 4-20mA treated intrinsically safe type to an instrument output signal, the output signal parameters such as the concentration of combustible gas, composition, temperature, liquid level, pressure vessel LNG detectors. The monitoring host mainly completes the continuous acquisition and processing on the initial safety parameters and fire parameters, modern methods of signal detection and processing of the signal collected by the state, analysis, and timely forecasts and take measures to deal with the accident, connection and remote control linkage effectively start site fire fighting equipment by DC hard line, the implementation of fire operation.

3. Monitoring system software implementation

The system application software adopts the modular programming mode, mainly including the main control module and the accident processing module, the information communication module, the fire management module and other functional modules. The functions of each module are as follows:

(1) main control module of the system. Mainly complete data acquisition and processing, alarm judgment and linkage control output, automatic and manual control mode switching, system management.

(2) accident disposal module. According to the monitoring data, the analysis and prediction of the accident status in the monitoring area is completed, the process safety is operated, controlled and disposed of the emergency, and the disaster relief plan is implemented.

(3) information communication module. It mainly completes communication protocol management, data communication control, remote remote networking.

(4) fire management module. The system operation management, equipment operation management, fire prevention management and data storage are mainly completed.