Steam heater

Stea.dy-Sta.teFeedforwa.rd, The simplest form of feedforward (FF) control utilizes a steady-state energy or mass balance to determine the appropriate manipulated variable adjustment. This form of feedforward control does not account for the process dynamics of the disturbance or manipulated variables on the controlled variable. Consider the steam heater shown ia Figure 15. If a steady-state feedforward control is designed to compensate for feed rate disturbances, then a steady-state energy balance around the heater yields ... 

Applications Most PHE applications are liquid-liquid seiwices but there are numerous steam heater and evaporator uses from their heritage in the food industry. Industrial users typically have chevron style channel plates while some food apphcations are washboard style. 

Note Alarms and shutdowns as shown are not to be considered as meeting any minimum safety requirement but are shown as representative of types used for controi systems. Schematic Alarm/Shutdown Hydrocarbon Low Pressure Hot oil or Glycol Amine Label Description Line Heater Reboiler Steam Heater Salt Heater Reboiler Reboiler ... 

Pumparound Flow Failure - The relief requirement is the vaporization rate caused by an amount of heat equal to that removed in the pumparound circuit. The latent heat of vaporization would correspond to the temperature and pressure at PR valve relieving conditions. "Pinchout" of steam heaters may be considered. 

For coolers, condensers, steam heaters and reboilers. The effluent cooling water and condensate are typically discharged as follows ... 

Figure 10-163. Constant flow direct steam heater (variable flow also available.) (Used by permission Cat. CF-5924 P. Pick " Heaters, Inc.)...

For large heat transfer duties, it is good practice to recover the steam that is flashed as the condensate reduces in pressure. Such an arrangement is shown in Figure 23.19. Steam enters the steam heater and condensate (in practice, with some steam) passes through the trap. Flashing occurs before the mixture enters a settling drum that allows the flash steam to be separated from the condensate. The flash steam would then be fed to a steam main at the appropriate pressure. 

Pickering Reactor Primary Circuit BHWP Steam Heater... 

In the first years of operation of the Bruce Heavy Water Plant (BHWP) deposition of iron pyrite, FeS2, necessitated frequent cleaning of the dehumidifier steam heaters. The iron... 

Option 3 An electric immersion or steam heater is optional... 

However, this system was abandoned because location of the steam heater inside the adsorber was not sufficiently safe. The modified system now most widely used is described below. 

Air, blown through a steam heater situated in the lower part of the drier, is warmed and then flows to the upper pari of the unit in co-and counter-current with the cotton. It has been found that application of the counter-current principle can readily cause a blockage in the lower part of the drier. 

The reaction mixture is pumped away from the reactor with an alkymer transfer pump, through a steam heater and an orifice mixer into the alkymer wash and surge tank. Dilute caustic solution is recirculated from the a.w.s. tank through the orifice mixer. Makeup of caustic is from a dilute caustic storage tank. Spent caustic is intermittently drained off to the sewer. The a.w.s. tank has an internal weir. The caustic solution settles and is removed at the left of the weir the alkymer overflows the weir and is stored in the right-hand portion of the tank until amount sufficient for charging the still has accumulated. 

Four classes of this kind of equipment are considered heat exchangers without phase change, steam heaters, condensers, and vaporizers or reboilers. These arc grouped together with descriptions in Figures 3.8-3.11. Where applicable, comments are made about the utility of the particular method. In these heat... 

Figure 3.9. Steam heaters, (a) Flow of steam is controlled off the PF outlet temperature, and condensate is removed with a steam trap or under liquid level control. Subject to difficulties when condensation pressure is below atmospheric, (b) Temperature control on the condensate removal has the effect of varying the amount of flooding of the heat transfer surface and hence the rate of condensation. Because the flow of condensate through the valve is relatively slow, this mode of control is sluggish compared with (a). However, the liquid valve is cheaper than the vapor one. (c) Bypass of process fluid around the exchanger. The condensing pressure is maintained above atmospheric so that the trap can discharge freely, (d) Cascade control. The steam pressure responds quickly to upsets in steam supply conditions. The more sluggish PF temperature is used to adjust the pressure so as to maintain the proper rate of heat transfer.

Feed to a spray dryer contains 20% solids and is to be dried to 5% moisture at the rate of 500 lb/hr of product. Pilot plant data show that a residence time of 6 sec is needed with inlet air of 230T, H = 0.008 lb/lb, and exit at 100°F. Ambient air is at 70°F and is heated with steam. Enthalpy loss to the surroundings is 10% of the heat load on the steam heater. The vessel is to have a 60° cone. Air rate and vessel dimensions will be found. 

Naphtha that is either naturally sweet (no odor) or has been treated until sweet is subdivided into several fractions in efficient fractional distillation towers, frequency called column steam stills. A typical arrangement consists of primary and secondary fractional distillation towers and a stripper. Heavy naphtha, for example, is heated by a steam heater and passed into the primary tower, which is usually operated under vacuum. The vacuum permits vaporization of the naphtha at the temperatures obtainable from the steam heater. 

The transfer of heat is one of the most basic and best-understood unit operations. Heat can be transferred between the same phases (liquid-liquid, gas-gas) or phase change can occur on either the process side (in the case of condensers, evaporators, and reboilers) or the utility side (in the case of steam heater) of the heat exchanger. 

In a feedback configuration the controlled variable (temperature) has to be upset before correction can take place. Feedforward is a mode of control that corrects for a disturbance before it can cause an upset. Figure 2.108 illustrates feedforward control of a steam heater. The feedforward portion of the loop detects the major load variables (the flow and temperature of the entering process fluid) and calculates the required steam flow (Ws) as a function of these variables. When the process flow increases, it is matched with an equal increase in the steam flow controller set point. Because instantaneous response is not possible, dynamic correction by a lead-lag element is provided. 

In feedforward optimization of steam heaters, major load variations (Tj and W) are corrected by the feedforward portion of the loop, leaving only the minor load variables for feedback correction. 

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