2000 Hook-up Book

How to Size Temperature and Pressure Control Valves

Calculating Condensate Loads When the normal condensate load is not known, the load can be approximately determined by calculations using the following formula. General Usage Formulae Heating water with steam (Exchangers)* lb/h Condensate = GPM x (1.1) x Temperature Rise °F 2 Heating fuel oil with steam lb/h Condensate = GPM x (1.1) x Temperature Rise °F 4 Heating air with steam coils lb/h Condensate = CFM x Temperature Rise °F 800 Steam Radiation lb/h Condensate = Sq. Ft. EDR 4 *Delete the (1.1) factor when steam is injected directly into water Specialized Applications Sterilizers, Autoclaves,

Valve Sizing For Steam Satisfactory control of steam flow to give required pressures in steam lines or steam spaces, or required temperatures in heated fluids, depends greatly on selecting the most appropriate size of valve for the application. An oversized valve tends to hunt, with the controlled value (pressure or tempera ture), oscillating on either side of the desired control point. It will always seek to operate with the valve disc nearer to the seat than a smaller valve which has to be further open to pass the required flow. Operation with the disc near to the seat increases the likelihood that any droplets of water in the steam supply will give rise to wiredrawing. An undersized valve will simply unable to meet peak load require ments, startup times will be extended and the steam-using equipment will be unable to provide the required output. A valve size should not be deter mined by the size of the piping into which it is to be fitted. A pressure drop through a steam valve seat of even a few psi means that the steam moves through the seat at high velocity. Valve discs and seats are usually hardened materials to withstand such conditions. The velocities acceptable in the piping are much lower if erosion of the pipes themselves is to be avoided. Equally, the pressure drop of a few psi through the valve would imply a much greater pres sure drop along a length of pipe if the same velocity were maintained, and usually insufficient pressure would be left for the steam-using equipment to be able to meet the load. Steam valves should be selected on the basis of the required steam flow capacity (lb/h) needed to pass, the inlet pressure of the steam supply at the valve, and the pressure drop which can be allowed across the valve. In most cases, proper sizing will lead to the use of valves which are smaller than the pipework on either side. Steam Jacketed Dryers lb/h Condensate = 1000 (Wi - Wf) + (Wi x ∆ T) L Wi = Initial weight of the material—lb/h Wf = Final weight of the material—lb/h ( ∆ )T = Temperature rise of the material °F L = Latent heat of steam Btu/lb Note: The condensate load to heat the equipment must be added to the condensate load for heating the material. Use same formula.

SYSTEM DESIGN

Retorts Heating Solid Material lb/h Condensate = W x Cp x ∆ T L x t

W = Weight of material—lbs. Cp = Specific heat of the material ( ∆ )T = Temperature rise of the material °F L = Latent heat of steam Btu/lb t = Time in hours Heating Liquids in Steam Jacketed Kettles and Steam Heated Tanks lb/h Condensate = G x s.g. x Cp x ( ∆ )T x 8.3 L x t G = Gallons of liquid to be heated s.g. = Specific gravity of the liquid Cp = Specific heat of the liquid ( ∆ )T = Temperature rise of the liquid °F L = Latent heat of the steam Btu/lb t = Time in hours

Heating Air with Steam; Pipe Coils and Radiation lb/h Condensate = A x U x ( ∆ )T L

A = Area of the heating surface in square feet U = Heat transfer coefficient (2 for free convection) ( ∆ )T = Steam temperature minus the air temperature °F L = Latent heat of the steam Btu/lb

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