Tuesday, November 29, 2011

Control Valve Calculation

Today I will be a simple matter to calculate the amount of water needed to reduce the temperature of the superheat steam to come down to the desired temperature using the desuperheater as we know it.
- If the water is less than the amount needed to prevent a pharmacist in the superheat steam temperature down to the desired temperature.
- If the amount of water required to superheat steam, which can become saturated steam will be dry again by the saturated steam through the separator.

Therefore, by the basic equation of energy conservation. "Conservation of energy" to determine the amount of water they can find it easily.


Enthalpy into process = Enthalpy out of process.
McwHcw + MsHs = MsHd + McwHd.
Mcw = Ms (Hs-Hd) / (Hd-Hcw).


By that.
Cw = Mass flowrate of cooling water (kg / h).
Ms = Mass flowrate of superheated steam (kg / h).
Hs = Enthalpy at superheat condition (kJ / kg).
Hd = Enthalpy at desuperheated condition (kJ / kg).
Hcw = Enthalpy of cooling water at inlet connection (kJ / kg).
Sample quantities of steam to 10,000 kg / hr at 10 bar, temperatures Sat Temp + 5 C, a decrease from 300 C to use much water.


How do Steam Table.
Ms = Mass flowrate of superheated steam = 10000 kg / h.
Hs = Enthalpy at superheat condition = 3052 kJ / kg.
Hcw = Enthalpy of the cooling liquid = 4.2 kJ / kg ° C x 150 ° C = 630 kJ / kg.
Saturation temperature (Ts) at 10 bar a of 180 ° C,.
The desired temperature must be Ts + 5 ° C = 185 ° C.
Hd = (Enthalpy at desuperheated condition (kJ / kg) = 2829 kJ / kg.
From the equation given.


Mcw = 10000x (3052 - 2791) / (2791-630).
Mcw = 1208 kg / h.


Therefore desuperheated steam = 10000 + 1208 kg / h = 11208 kg / h.
However, due to problems with the steam flow rate of 10000 kg / h, so the superheated steam flow rate can be determined by the ratio of the post.
10000/11208 = Ms/10000.
Ms = 8923 kg / hr.


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Control Valve: ISA-75.01 Flow Equations for Sizing Control Valves.


Usually, the size of the control valve to the vendor, then it calculates the value (Cv and Fd is the vendor's catalogue), but the purpose of this article so it can be calculated initially on their own. I will provide important information that I have. ANSI/ISA-75.01-1985 (R1995), Flow Equations for Sizing Control Valves. ISA - The Instrumentation, Systems, and Automation Society, by the Table D-1 of ANSI/ISA-75.01-1985. This shows the value of any Valve capacity factors that can be put in the value of my ISA.

Valve TypeTrim TypeFlow DirectionXtFlFdCv/d 2
GLOBE Single PortPorted PlugEither0.750.91.09.5
"Contoured PlugOpen0.720.91.011
""Close0.550.81.011
"Characterized CageOpen0.750.91.014
""Close0.700.851.016
"Wing GuidedEither0.750.91.011
GLOBE Double PortPorted PlugEither0.750.90.712.5
"Contoured PlugEither0.700.850.713
"Wing GuidedEither0.750.90.714
GLOBE RotaryEccentric Spherical PlugOpen0.610.851.012
""Close0.400.681.013.5
ANGLEContoured PlugOpen0.720.91.017
""Close0.650.81.020
"Characterized PlugOpen0.650.851.012
""Close0.600.81.012
"VenturiClose0.200.51.022
BALLSegmentalOpen0.250.61.025
"Standard 80% PortEither0.150.551.030
BUTTERFLY60 0 alignedEither0.380.680.717.5
"Fluted VaneEither0.410.70.725
"90 0Offset SeatEither0.350.600.729

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