Shell-Tube Heat Exchanger

Abstract- In many industrial processes and operations heat exchangers are one of the simplest and important unit for the transfer of thermal energy. There are different types of heat exchangers used in industries; the Shell and Tube Heat Exchanger system being the most common since it can sustain wide range of temperature and pressure. The main purpose of heat exchanger is to maintain specific temperature conditions, which is achieved by controlling the exit temperature of the process fluid in response to variations of the operating conditions. In this paper, Model based control technique is employed ;Internal Model Controller (IMC) combined with disturbance rejection function and Internal Model based Proportional-Integral-Derivative(PID) controller

Our paper presents an advanced control strategy that uses the Internal Model Controller and Internal Model based PID controller. This paper considers a single-input single-output model of Shell and Tube heat exchanger. The outlet temperature of the heat exchanger system has to be kept at a desired setpoint according to a process requirement.

II. SHELL AND TUBE HEAT EXCHANGER SYSTEM

The schematic diagram of temperature control of a shell and tube heat exchanger is shown in Fig. 1.The process fluid is supplied to the heat exchanger system using a pump and a nonreturning valve. The super-heated steam comes from the boiler and flows through the tubes, whereas the process fluids flow through the shell side of the heat exchanger system. After the steams heat up the process fluid, the condensed steam goes out of the heat exchanger system [2].

The output temperature is continuously monitored by 2-Wire

RTD sensor implemented in the feedback closed loop path. The output of the sensor is in voltage form which is converted into standard 4-20 mA output which is proportional to the temperature. The PC based controller compares the

Modeling of Valve Top and Positioner

The position of the stem (or, equivalently, of the plug at the end of the stem) will determine the size of the opening for flow and consequently the size of the flow (flow rate) determined by the balance of all forces acting on it [6][8].

푃푑A = kx+C

푑푥

푑푡

(20)

These forces are:

PdA=Force exerted by the compressed air at the top of the diaphragm kx =Force exerted by the spring attached to the stem and the diaphragm C dx dt

=Frictional force exerted upward and resulting from the close contact of the stem with valve packing where: A – Area of the Diaphragm, 푃푑 – Pressure acting on diaphragm, x – Displacement, k – Hook’s constant

The Transfer Function Of the valve from (20) is

퐾푉

1+푇S

(21)

Let the control valve has a maximum travel of 1.56mm, and time constant of 3 sec. The nominal pressure range of the valve is 3 to 15