Problems encountered during operation
The main problem of the system throughout the heating season is the insufficient heat exchange capacity of the spike heater. The heat exchanger is installed in the circulating water supply bypass, using double bellows type heat exchanger, its design parameters: flow rate G = 1500t / h, heat transfer area F = 170m2, the design of the inlet steam parameter t = 180 ℃, P = 0.2MPa, the circulating water inlet and outlet design temperature difference △ t = 15 ℃. The heat exchanger is put into operation during the period, the temperature difference between the inlet and outlet water △ t is only about 5 ℃, although adjusted, the effect is not great, and its role can not be given full play.
Cause analysis
(A) heat exchanger selection is too small, resulting in insufficient heat transfer
The heat exchanger manufacturer to provide the heat transfer area of 170m2, we calibrated the heat exchanger heat transfer area calculation:
1, the heat required to heat the feed water:
From the above, the actual heat exchanger area to meet the heat transfer requirements, so the heat exchanger heat transfer is not the problem of insufficient heat exchanger heat transfer area caused by insufficient.
(B) the heat exchanger air is not discharged
The heat exchanger body is not designed to pipe course, shell course of the high point of the bleeder valve, so to a certain extent will affect the heat transfer effect. In order to reduce the impact, we are in the entire heating system, the supply and return pipelines are equipped with the highest point of the bleeder valve, in the initial operation of the system when filling and operation of the occasional release of steam, to minimize the existence of air in the system to affect the effect of heat transfer.
(C) the heat exchanger there is scaling phenomenon
Heat exchanger scaling, will have a great impact on the heat exchanger heat transfer effect, resulting in a reduction in the heat transfer coefficient, heat transfer efficiency is greatly reduced, the export of water temperature. In order to avoid heat exchanger scaling, the choice of a double bellows heat exchanger, the heat exchanger heat pipe special structure, so that the water in the tube flow is turbulent flow state, the flow rate is high, it is not easy to scale. In the system shutdown, we will be the heater disassembled to check the internal basic no scaling phenomenon.
(iv) Insufficient steam
In the system, steam metering device using vortex flowmeter, due to installation conditions, can not meet the requirements of the steam metering device installation, for the amount of steam into the heat exchanger can not get accurate data.
(E) waterway clogging
Heat exchanger water circuit blockage will reduce the amount of circulating water flowing through the heat exchanger, resulting in a large temperature difference between the heat exchanger water circuit and the incoming water, the pressure difference, and high hydrophobic temperature. However, in actual operation, the heat exchanger import and export pressure difference △ P = 0.02MPa or so, the manufacturer provides the pipe resistance for △ P = 0.04Mpa, from the analysis of the operating conditions, the possibility of waterway blockage. In the disassembly of the heater in the inspection of the pipeline inspection, did not find the phenomenon of blockage.
(F) poor hydrophobicity
The system in operation there is a phenomenon of poor condensate drainage, heat exchanger water level often to the high limit, must open the bypass for trapping, otherwise the heat exchanger water level rises, the steam side of the steam pressure rises, resulting in the heater steam side of the safety valve jump. The existence of this situation, so that the operator can only reduce the amount of feed steam, and long-term open bypass operation, which greatly reduces the heat transfer efficiency of the heat exchanger. The trap was initially suspected to be clogged, but no abnormality was found after disassembling and inspecting the trap, which required a calibration calculation of the trap's discharge capacity.
The solution and future attention
Combining the above factors, the solution to the problem of insufficient heat exchange for the heat exchanger is as follows:
1, re-traps for the selection of traps, traps in the trap pipeline to add a trap regulating valve, the trap is based on the heater's water level changes, through the DDZ-II type electronic adjustment system to achieve regulation and control. Heater water level signal through the differential pressure transmitter, proportional integral unit, operating unit, and finally by the electric actuator to manipulate the regulating valve, by adjusting the size of the valve opening to control the size of the water supply. This will enable the heat exchanger trap water discharged in a timely manner to ensure that the effect of heat transfer.
2, daily attention to control the quality of circulating water, strengthen water quality supervision, minimise the occurrence of heat exchanger scaling phenomenon;
3, for the system of steam metering device, looking for ways to solve as soon as possible;
4, regular disassembly of the heater inspection or backwash, remove debris in the heater, improve the efficiency of the heater;
In addition, when the system is filled with water at the beginning of the commissioning of the equipment, the air in the heater must be released to avoid affecting the quality of heat transfer.
