With features of energy saving and environmental protection, heat transfer fluid has been used in many fields, including oil, coking, energy and chemical industry, food manufacture, pharmacy and machinery industry. Typical features of heat transfer fluid heating are high temperature with low pressure and high heat transfer efficiency. As all the other chemical production processes, system safety is the first priority of fluid application. Fluid degradation is the chief culprit of system accidents. It is suggested to pay much more attention to the system overheating which could easily cause fluid degradation.
The effective measure to avoid fluid overheating is to control fluid flow velocity properly. Liquid phase fluid heating system mostly uses forced circulation operation which makes flow velocity in heated pipeline a very important parameter. The setting of fluid flow velocity is related to fluid boiler design and system safety consideration.
The design of fluid boiler and system should be in compliance with standards and requirements. According to Boiler Safety Technical Supervision Administration Regulation, to avoid fluid deterioration and coking in liquid phase system, fluid velocity in heating surface should reach a fixed value, which is fluid velocity in radiation heating surface should not be less than 2.0m/s and fluid velocity in convection heating surface should not be less than 1.5m/s. It is also suggested to install the bypass regulating valve to control fluid velocity automatically during system technical load fluctuation.
The safe fluid velocity should also conform to the economic consideration. The increase of fluid velocity decreases the fluid duration in heating boiler which reduces heat transfer efficiency and raises pump power and operating costs. It is necessary to consider operation costs and system safety in setting of fluid velocity.