CHE302 LECTURE III ACTUATOR AND CONTROL VALVE SELECTION. Professor Dae Ryook Yang INTRODUCTION TO ACTUATOR

Size: px

Start display at page:

Download "CHE302 LECTURE III ACTUATOR AND CONTROL VALVE SELECTION. Professor Dae Ryook Yang INTRODUCTION TO ACTUATOR"

Rosamund Grant
5 years ago
Views:

1 CHE30 LECTURE III ACTUATOR AND CONTROL VALVE SELECTION Profeor Dae Ryook Yang Fall 001 Dept. of Chemical and Biological Engineering Korea Univerity CHE30 Proce Dynamic and Control Korea Univerity 3-1 INTRODUCTION TO ACTUATOR What i actuator? Actuator convert the command ignal from controller or higher-level component into phyical adjutment in adjutable proce variable Command ignal (V, ma, pig, ) Actuator Adjutment of Phyical Variable (F, motor peed, ) Actuator type Control valve: pneumatic, electric, hydraulic Electric heater output: SCR, thyritor Pump/Motor peed: inverter Diplacement: pneumatic, electric, hydraulic CHE30 Proce Dynamic and Control Korea Univerity 3-

2 Actuator ACTUATOR AND D/A CONVERTER Convert the indutrial tandard ignal to action uch a valve opening, power level, diplacement, and etc. Standard intrumentation ignal level and ignal converion tranmitter are ued. Actuator power Pneumatic: imple, low cot, fat, low torque, hyterei Electric: motor and gear box, high torque, low Hydraulic: high torque, fat, expenive Digital-to-Analog (D/A) converter (+Hold) Digital ignal i converted to continuou ignal and the ignal i hold until the ignal i changed Specification: hold type, reolution (8bit, 1bit, 16bit) CHE30 Proce Dynamic and Control Korea Univerity 3-3 CONTROL VALVE Valve+Actuator Valve opening i adjuted by an actuator Pneumatic Control Valve Uually 3~15pig ignal i provided. I/P tranmitter convert 4~0mA ignal to 3~15pig pneumatic ignal via 0pig upply air Yoke Valve tem Inlet intrumentation air Diaphragm Actuator pring Travel indicator Valve plug Packing Valve eat CHE30 Proce Dynamic and Control Korea Univerity 3-4

CONTROL VALVE IMPLEMENTATION For the maintenance Bypa Block valve Intallation Horizontal Vertical Flange type Screw type Reducer may be required CHE30 Proce Dynamic and Control Korea Univerity 3-5

3 CONTROL VALVE IMPLEMENTATION For the maintenance Bypa Block valve Intallation Horizontal Vertical Flange type Screw type Reducer may be required CHE30 Proce Dynamic and Control Korea Univerity 3-5 AIR-TO-OPEN OR AIR-TO-CLOSE A air preure increae, the valve opening can become larger or maller Air-to-open (normally cloed, fail cloe): a the air P increae, the valve opening get larger Air-to-cloe (normally open, fail open): a the air P increae, the valve opening get maller The election hould be made baed on the afety conideration Furnace fuel valve hould be cloed in cae of utility failure Coolant valve in exothermic reactor hould be open in cae of utility failure CHE30 Proce Dynamic and Control Korea Univerity 3-6

CONTROL VALVE PACKING Packing i eential to maintain the ealing

lifetime of the packing Control action hould not be to vigorou in

Korea Univerity 3-7 CONTROL VALVE CLASSIFICATION Linear motion Globe

Split bodied Control Valve Gate Rotary motion Eccentric plug

4 CONTROL VALVE PACKING Packing i eential to maintain the ealing Packing ha to be replaced periodically Exceive uage may horten the lifetime of the packing Control action hould not be to vigorou in order to prevent the exceive wear CHE30 Proce Dynamic and Control Korea Univerity 3-7 CONTROL VALVE CLASSIFICATION Linear motion Globe Diaphragm way angle Single eated Double eated Pinch or clamp 3 way Split bodied Control Valve Gate Rotary motion Eccentric plug Butterfly Ball Butterfly Diaphragm Pinch Gate CHE30 Proce Dynamic and Control Korea Univerity 3-8

5 VALVE TYPES Globe valve rugged, uually the mot expenive, particularly in the larger ize, accurate and repeatable control, high preure drop Gate Valve liding dic (gate), ideal for high preure drop and high temperature application where operation i infrequent, multi-turn or long troke pneumatic and electro-hydraulic actuator are needed, poor control Ball Valve tight hutoff, high capacity with jut a quarter-turn to operate Butterfly Valve damper valve, mot economical valve, high torque required Diaphragm Valve implet, tight hutoff, iolated, ideal for corroive, lurry and anitary ervice. CHE30 Proce Dynamic and Control Korea Univerity 3-9 Baic Equation VALVE EQUATION Pv q( l) = Cv f ( l) 0 l 1 g where l i the valve tem poition. Valve coeff. (C v ) i decided by valve ize Valve trim type for different plug Linear: Square-Root (Quick Opening): Equal Percentage: f ( l ) = l f ( l) 1 = R l f ( l ) = l R: rangeability (ratio between minimum flow and maximum flow) the bigger R i, the more accurate CHE30 Proce Dynamic and Control Korea Univerity 3-10

6 VALVE TRIM(PLUG) TYPE Equal Percentage Mot commonly ued Ued where large preure drop i expected Linear Ued where fairly contant pre. drop i expected Ued for liquid level or flow loop Quick Opening Ued for frequently on-off ervice Ued where intantly large flow i needed CHE30 Proce Dynamic and Control Korea Univerity 3-11 VALVE FLOW CHARACTERISTICS Inherent characteritic Intalled characteritic All P i in valve: no P in proce Total P in a ytem i provided by a pump or compreor Change in valve opening flow change in proce change in P acro the valve Linear plug doe not lead to linear P behavior when intalled total P = kq P = P q v + P max total = g + C v kq max CHE30 Proce Dynamic and Control Korea Univerity 3-1

7 NONLINEAR BEHAVIOR Flow v. valve trim (intalled) Pv q( l) = Cv f ( l) 0 l 1 g where P = P v total P q = C max implicit nonlinear equation of flow and valve trim The pumping requirement ( P total ) i determined by thep in both proce and control valve at the max. flow max v g + kq kq CHE30 Proce Dynamic and Control Korea Univerity 3-13 VALVE SIZING Step1 Decide max. and min. flow of a fluid (rangeability for equal percentage valve) and P total Step Define a max. allowable P v when the valve i wide open It hould be 10~15% of P total or about 10pi whichever i greater Step3 Calculate the intalled valve characteritic It hould be linear around the region you want Step4 Adjut the pumping requirement ( P total ) and valve ize (C v ) o that the max. flow can be achieved and the curve i linear around the operating region Make ure that the P v when the valve i wide open i not over the limit in Step CHE30 Proce Dynamic and Control Korea Univerity 3-14

OTHER CONSIDERTIONS If pump characteritic curve i available For many pump, a flow increae, the pump dicharge preure i decreaed. Then the pump dicharge P ( P total ) will change with flow rate.

8 OTHER CONSIDERTIONS If pump characteritic curve i available For many pump, a flow increae, the pump dicharge preure i decreaed. Then the pump dicharge P ( P total ) will change with flow rate. Sonic flow and Choke flow When the P acro the valve i large, onic flow can occur. When P get larger, then choked flow occur, and the downtream preure doe not influence the flow rate. Thee two happen when the valve ha exceive preure drop. Alo, if the P i too high, flahing may occur. If lager valve i ued, there will be le P v and le pumping requirement ( P total ) i needed. However, the controllability of the flow i acrificed. (trade-off) A a rule of thumb, the P v hould be around 1/3~1/4 of P total at nominal flow rate. CHE30 Proce Dynamic and Control Korea Univerity 3-15 HYSTERESIS AND VALVE POSITIONER Hyterei Due to friction between the tem and packing, looe linkage, preure drop, tiction or etc. When the command ignal (pneumatic ignal) i going up and down, the flow rate will not be ame even though the command ignal i ame depending on the direction of ignal change. Remedy Change the command ignal with the ame direction by lowering or increaing it momentarily Ue valve poitioner Valve poitioner The valve poitioner i a controller which can ynchronize the command ignal and it correponding valve tep poition. By ue of valve poitioner, hyterei can be overcome. CHE30 Proce Dynamic and Control Korea Univerity 3-16

CHBE320 LECTURE III ACTUATOR AND CONTROL VALVE SELECTION. Professor Dae Ryook Yang

CHBE320 LECTURE III ACTUATOR AND CONTROL VALVE SELECTION Professor Dae Ryook Yang Spring 2018 Dept. of Chemical and Biological Engineering 3-1 Visit Actuator Road Map of the Lecture III + - Controller