Issues with heat tracing for instruments and condensate recovery
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This post was last edited by chensf123 on 2016-1-5 at 23:15. A few days ago, I saw some colleagues discussing matters related to insulation and heat preservation. Since our company is based in the south while our factory is located in the north, and our employees mostly come from the south and lack experience in maintenance work in northern regions, ensuring the safety of instrumentation and equipment through the winter has become a top priority during this season. We use low-pressure steam at 0.4 MPa for heating. Since the heating pipelines for instruments are generally small, the condensed water is collected and sent back to the water treatment unit. Due to the high resistance in the system, the heating effect is very poor; this year, heavy snowfall occurred in the north along with low temperatures, which caused many transmitters to be damaged by freezing as well as the measurement pipelines to crack. Since our company’s design institute is also a southern-based enterprise and lacks experience as well, we can only discharge most of the condensate directly into an open container and then pump it back using a booster pump. I wonder how things are on the ground for those of you in the north?
Since it is designed with steam tracing and the unit is large, converting it to electric tracing would require a massive effort; we have plenty of low-pressure steam available, and from a cost perspective, there is no need to switch to electric tracing.
4 kilograms of steam is acceptable; but has proper insulation been ensured after heating?
Is the instrument air produced in-house? Is the moisture content of the instrument air below 0.5?
Ethylene glycol antifreeze is commonly used for orifice plates and pressure measurement points; pressure measurement points can also use single-flange types with diaphragms and isolation fluids. For liquid level control, double flanges with diaphragms and isolation fluid are commonly used, or ethylene glycol antifreeze can also be employed. For heating glass plates, the heating tubes built into the glass plates themselves are generally not used. A shut-off valve and a check valve should be installed behind the sealed heat-traced trap. We also mostly use low-pressure steam at 0.4 MPa for heating; we employ self-pressured closed transportation, and the discharge pressure of the condensate is generally less than 0.1 MPa, with a maximum of no more than 0.18 MPa. I have seen that in two companies located further north (Xinjiang, Dalian), the condensate water is also collected together and then transported using power.
We are a petrochemical company in Daqing. In the past, freezing problems often occurred when steam was used for heating, but after switching to hot water heating with pressure applied by pumps, the problem was resolved; now there is no more freezing. However, steam is generally still required for the heating of instruments in tall towers.
Since our design firm is also a company based in the south, flange-mounted instruments are rarely used when selecting instruments; instead, pressure guiding tubes are employed for installation. The instruments that are affected by freezing are mostly those found in steam systems, such as drum level, steam pressure, and flow rates, as well as those in water systems.
All the condensate water from the equipment is collected in one tank and sent to the condensate water pipeline network for recovery
Use antifreeze for pressure measurement, add an insulation box around the instrument to ensure airtightness, and then try using electric heating.