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Steam energy savings——Part 2: Selection of steam traps. Technical Service Center of Hangzhou Watt Energy Saving Engineering Co., Ltd.; Steam technology engineer Li Shaopeng. As is known from the basic properties of steam, the heat contained in steam consists of sensible heat (the heat contained in the condensed water) and latent heat (the heat released or absorbed when steam evaporates or condenses). Compared to the latent heat of steam, only a small portion of the sensible heat is present in the condensed water. For heating efficiency, we usually utilize the latent heat (i.e., enthalpy of vaporization) released when steam turns into condensed water. When steam releases its latent heat and turns into condensed water, it is discharged through a drain valve. Part of the sensible heat contained in the condensed water may be released as secondary steam, while the remaining part is carried back to the boiler room by the condensed water for reuse. But in some situations, such as the insulation of storage tanks, the latent heat contained in this condensed water still has considerable value for utilization. For applications like this, thermostatic steam traps have been produced. We know that there are certain types of steam traps, such as thermodynamic traps, which not only prevent steam waste but also reduce the temperature of the condensed water, thereby making it possible to utilize the sensible heat contained in the process condensate. This type of steam trap is mainly used in some non-critical equipment, such as heat tracing pipes and overhe sized heating coils. Sensible heat can be absorbed or used to heat another process. Alternatively, a cooling tube can be installed in front of the drain valve to ensure an accurate condensate discharge temperature. In many applications, the accumulation of water is not allowed, as it can cause the following problems: • Reduced production capacity • Corrosion of condensate pipes • Inadequate drainage from main pipes. Therefore, for critical equipment that requires the discharge of condensate at steam saturation temperature, such as: • Temperature control equipment (e.g., heat exchangers). • Equipment with a small steam heating space. Only thermodynamic steam traps, inverted bucket steam traps, or float-type steam traps can be considered; other types of steam traps will result in supercooled condensate. Condition of steam equipment: We know that it is necessary to remove air from the system promptly (this is the case in most systems, especially during startup), and in such situations thermal expansion steam traps are not suitable as they allow for very slow air release (unless a separate vent valve is installed). Watt’s thermostatic steam traps, float-type steam traps with venting devices, and thermally inverted drum steam traps exhibit excellent venting performance. The exact model of Hangzhou Watt steam trap can be selected based on its ability to handle the following issues: • Water hammer • Corrosion and impurities. Water hammer should be avoided from the design stage of any equipment. If it does occur, some types of steam traps have better water hammer resistance than other types. Generally, steam traps are affected by contaminants in the flow or within the pipes; therefore, the advantage is obvious when a steam trap is equipped with an internal filter, such as in Watt’s bimetallic steam traps. Since the discharge orifice of a steam trap is relatively small and prone to being blocked by impurities or welding slag in the pipes, it is recommended that a filter be installed upstream of any type of steam trap. Steam traps that meet specific industrial and application requirements – Different types of steam traps can satisfy special industrial and application needs. Stainless steel steam traps designed specifically for clean steam systems can be used in industries such as food and pharmaceuticals. There are also other steam traps designed specifically for certain processes; for example, the FQ float-type steam trap is intended for use in sugar-making processes with low pressure and high load. FQ is actually a hybrid type of drain valve: it features a hole of fixed size that handles stable high loads during operation, along with a float mechanism that takes action when water accumulates. If properly selected, installed, and maintained, the steam traps manufactured by Hangzhou Watt can operate without failure for a long time. The steam trap installed years ago is still working as well as it did on the day it was installed. Selection Factors affecting the selection of steam traps. It is very important to select steam traps correctly; we cannot simply determine the size of the trap based on the diameter of the pipeline. The following information is needed to select the proper steam trap: • Maximum pressure of the steam system • Maximum/minimum pressure difference • Condensate discharge temperature • Condensate load during operation • Safety factors at startup and low pressure. The maximum system pressure is used to determine whether the valve body and its internal components can meet the application requirements. Maximum Allowable Pressure (PMA): Select a check valve that can withstand the system’s maximum allowable pressure or design pressure. The steam trap does not operate at this pressure, but it should be able to withstand it. These are the PMA (maximum allowable pressure) and PMO (maximum operating pressure) indicated on the nameplate of a SpiraMax steam trap. When selecting a steam trap, both PMA and TMA need to be taken into consideration. . For example, for 1½” or 2” FT14, the PMA is 16 bar and the TMA is 220ºC; at 16 bar the TMO is only 120ºC, while at 220ºC the PMO is 13 bar. Pressure difference (P): The maximum pressure difference refers to the greatest disparity in pressure between the inlet pressure and the condensate recovery pipeline. The steam trap should be able to open at this pressure. Inlet pressure: The inlet pressure can be the pressure in the boiler or steam main, or it can be the pressure after reduction at a pressure reduction station. Discharge pressure: The discharge pressure can be: • Atmospheric pressure • Below atmospheric pressure (vacuum) • Above atmospheric pressure, which is determined by pipe friction, the rise in pressure in the pipeline behind the check valve, or the pressure in the return pipeline. For critical equipment, both the maximum and minimum pressure differences across the steam trap need to be known. If the steam pressure at the inlet of the steam trap is 7 bar and the condensate is discharged directly to the atmosphere, then the pressure difference ΔP is 7 bar ； If the condensate is discharged into a recovery pipeline at a certain pressure, then P is smaller. The minimum pressure difference is the main factor affecting the condensate discharge rate through the steam trap. Generally, if the ΔP of the steam trap is low, the discharge volume will decrease. A high pressure difference helps condensate water pass through the drain valve. If the pressure difference is very small or negative pressure (vacuum) occurs for some reason, the check valve will be in a ‘flow-loss’ state. For some heating processes, the accumulation of condensate water is not allowed to prevent uneven heating. It should be noted that, typically during the startup phase, the upstream pressure rises slowly and the pressure difference is also low. A positive pressure difference facilitates the drainage of condensate water. When selecting a device, the pressure difference under worst-case conditions should be taken into account, especially in cases where there is a lift pipe downstream of the temperature control equipment or the steam trap; in such situations, a float-type steam trap/pump combination can be installed. The temperature of the condensate also affects the flow rate of water passing through the steam trap. The lower the condensate temperature, the more condensate can pass through the steam trap. This is mainly because the pressure drop as hot condensate water flows through the drain orifice of the check valve generates flash vapor; the higher the temperature of the condensate water, the more flash vapor is produced, which in turn creates a certain degree of obstruction. Therefore, many displacement charts show the discharge volumes of hot condensate and cold condensate. Rated load: The standard steam-using equipment’s nameplate will indicate the rated condensate discharge volume; if such data are not available, it can be calculated or determined through actual measurement. Regarding the maximum condensate load, the amount of condensate produced by different types of steam-using equipment varies at different operating stages.