Principle of operation
During gas pressure regulation, gas temperature drop takes place as a consequence of gas depressurisation (Joule-Thompson effect). This rapid temperature drop may cause frosting and even freezing of regulating devices, especially of the remote control units controlling the pressure regulators installed in high-pressure regulating stations. In order to maintain trouble-free operation of gas pressure regulating stations, it is necessary to increase gas temperature prior to regulation to assure a gas temperature after regulation within +5 to +10oC. One of the most commonly used methods of natural gas heating in pressure regulating stations is the application of heat exchangers with hot fluid used as a heating medium.
Gas heating is a result of heat transfer between the heating medium and the gas flowing through the tube bundle (coil). The heating medium temperature in the heat exchanger is controlled depending on gas temperature downstream the regulating device. Adding a circulation pump to the heating medium circuit improves heat transfer and control’s accuracy. The circulation pump increases the efficiency of heat exchanging surface’s exploitation and allows to reduce heating medium tubes’ diameter.
Work parameters of heat exchangers
Inlet (design) gas pressure:
Standard: 16 – 25 – 63 – 100 bar
• design pressure of the heating section: standard 6 – 63 bar
• inlet temperature: +90oC
• outlet temperature: +70oC
Heat exchangers are equipped with a pipe connector located on the shell side, to connect a safety equipment. If a tube is damaged, gas may be immediately vented into the atmosphere, either via a safety head or safety valve. In standard applications the pipe connector is designed with a flat flange PN16. When the shell side’s design pressure is the same as gas section’s design pressure, safety is provided by application of HON (RMG) 790 valve set for the maximal pressure of the heating medium in the boiler system. Gas escaping through the damaged tube is captured inside the shell side of the heat exchanger.
Construction and principle of operation
Heat exchangers in the basic configuration have coils welded into a mesh bottom, located between the tube side flange and the heating medium jacket flange. These parts may, at any time, be individually replaced. Cold gas flows through the inlet pipe into the coil. After being heated during transport through the coil, gas leaves the heat exchanger through the outlet pipe. The heating medium flows through a number of baffles, leading it round the coil. The tube bundles (seamless, R13,5 x 2) are welded into the mesh bottom designed (calculated) accordingly to the gas pressure. The wall thickness of all tube bundles is 2 mm. Corrosion allowance of tube bundles is 1 mm.
The tube side of the heat exchanger is equipped with connector pipes for draining condensate. The mesh bottom is equipped with a drain valve to drain remains of heating medium within the space below the outlet connector.
GAZOMET products pressure equipment according to quality system under Pressure Equipment Directive 2014/68/EU.
Thereby GAZOMET is entitled to mark the produced pressure equipment with CE mark.