Selection of Steam Traps

Steam is used in many chemical industries for the following  

Steam can supply a large amount of heat over long distances (as it has a large latent heat and does not need a pump). 

The following factors should be considered when selecting steam traps  

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Thus, selection and sizing of steam traps are critical for the management program. The steam trap should be sized for either start-up or operating conditions, depending on how often the unit will start up. If it is sized for operating conditions, then additional manual drainage should be considered for start-up. Six factors are listed in detail for selection of steam traps (Kenney, 1984) ... 

Determine the condensate load. The first step in selecting a steam trap for any type of equipment is determination of the condensate load. Use the following general procedure. a. Solid materials in autoclaves, retorts, and sterilizers. How much condensate is formed when 2000 lb of solid material with a specific heat of 1.0 is processed in 15 min at 240°F by 25-psig steam from an initial temperature of 60°F in an insulated steel retort ... 

On this basis, the selection of a group of steam traps to handle all steam tracing situations is possible. Actually this consists of a 3/8-inch nominal size trap but many steam trap manufacturers rate their traps by orifice size rather than by connection size. Suitable traps should have 150 psig steam condensate capacities from 350 to 600 pounds per hour at saturation temperature, and from 550 to 850 pounds per hour at 30°F below saturation temperature. Using 15 psig steam, the condensate capacity should range between 135 and 250 pounds per hour at saturation temperature and from 225 to 400 pounds per hour at 30°F below saturation temperature. 

Maximum superficial condensate velocities are about 25 m s . In a given line, the velocity increases as the pressure drops and more liquid vaporizes. Vendors of steam traps and condensate systems can provide guidance and line-sizing charts. Water lines usually have velocities up to 3ms . The designer must consider water hammer as well as velocity and pressure drop. Selection of valves and their closure time becomes important. Compressed air usually is transported at 5-8 m s. ... 

Considerations for selecting the right type of steam trap are as follows ... 

Each type and size of steam trap has a specified capacity for the amount of condensate and noncompressible gas that it can handle. Care must be taken to ensure that the proper steam trap is selected to meet the application s... 

As discussed previously, each type of steam trap has a range of steam pressures that it can effectively handle. Therefore, each application must be cateliilly evaluated to determine the normal and maximum pressures that will be generated by the steam system. Traps must be selected for the worst-case scenario. 

Fig. 6. Hie effect of vanaKiium on the selectivities of steam deactivated ocmneccial caitalysts witdi and without a vanadium trap, (a) MAT specific oolos yields and (b) MAT hydrogen yield.

For a steam coil to operate efficiently, it must have all the latent heat in the steam. This is achieved by the use of a steam trap. The correct trap type must be selected for the particular application in order to prevent waterlogging. All condensate, air, or other noncondensable must be removed from the system without delay otherwise,... 

Partial waterlogging of heater batteries can lead to early failure due to differential thermal expansion. Steam trap selection should take account of this. 

Select steam traps for the following five types of equipment (1) where the steam directly heats solid materials, as in autoclaves, retorts, and sterilizers (2) where the steam indirectly heats a liquid through a metallic surface, as in heat exchangers and kettles where the quantity of liquid heated is known and unknown (3) where the steam indirectly heats a solid through a metallic surface, as in dryers using cylinders or chambers and platen presses and (4) where the steam indirectly heats air through metallic surfaces, as in unit heaters, pipe coils, and radiators. 

Select the trap size based on the load and steam pressure. Obtain a chart or tabulation of trap capacities published by the manufacturer whose trap will be used. Figure 6.8 is a capacity chart for one type of bucket trap manufactured by Armstrong Machine Works. Table 6.15 shows typical capacities of impulse traps manufactured by the Yarway Company. Be sure to use up-to-date vendor data. 

The boiler itself should be very efficient to generate steam and for this preparation of oil, air to fuel ratio, stack temperature of flue gases, conversion of furnace oil to LSHS oil, maximum condensate recovery, cleaning of the fire side, replacement of old boilers etc. are the various important factors to be taken care-of. Factors responsible for optimum consumption of steam such as supply of steam at correct pressure, provision of pressure reducing valves, water separators in steam lines for supply of dry steams at requisite pressure, selection of trap of right type and size for efficient recovery of condensate etc. should be considered for the saving of thermal energy. 

Freeze Drying. Freeze drying or lyophilization, with trapping of the volatiles that come over with the water vapor (31), would seem to have some advantages because of the mild conditions used. However, there is considerable selection of volatiles because the intact tissues act as a barrier to many volatiles whereas they are permeable to water. Freeze drying can also be considered a type of vacuum steam distillation. 

A typical steam tracing system is shown in Figure 7-84. The keystone of this system is the steam trap. Correct selection and application of other components is to no avail if the steam trap is improperly chosen. Selection must be based on two choices type and size of the trap. 

Pressure tests of pipelines, jackets, steam coils, and arrangement to isolate and take out coils for maintenance are necessary. Steam traps shall be selected for the removal of condensate as soon as formed. There shall be no cooling of condensate in the jacket or coils (unless system is specially designed to recover heat from hot condensate also). 

In order to compensate for these variations in operating conditions, the designer uses a capacity safety factor to increase the calculated condensate load. This safety factor should be selected with care. One short-cut method that should be avoided sizing steam traps to equal line size. This practice is never a substitute for analyzing process conditions it invariably leads to specification of the wrong size steam trap. 

The required orifice continuous flow capacity is determined at steam chest pressure to condensate system pressure at a flow 6 to 8 times design. If designed for normal flow the trap would have to be open 100% of the time. Then, as stated above, a body size is selected that can contain the required orifice (not be above the stated... 

A simplified cyclic test (Mitchell method followed by cyclic propylene steaming) has been proposed which addresses the redox aging of the metal, but not the non-uniform laydown and age distribution of metals on the catalyst. Under actual FCC conditions, the penetration and age profile of the metals will influence the efficiency of the catalyst metal trapping function [23,39,40] and consequently catalyst activity and selectivity. 

For this study a section of Zybza field was selected which had sufficient number of wells for steam injection, for oil recovery and for conduct of different temperature surveys. The section was located on a large stratigraphic trap in the central part of the field. A structure contour map of the section was drawn up, and all the different investigations preliminary to block-cyclic steaming were completed before the start-up of actual steam treatment. 

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