Distillation Column Control
Distillation Column Control Fundamentals –
Tnomenclature used in this paper and points out the five valves available to control column. There are 5 degrees of freedom in typical binary distillation column which are represented by feed valve, steam valve, reflux valve, distillate valve, and bottoms valve.
The five valves are used . First, either the feed, bottoms, or distillate rate is set independently to define production rate of column, thereby eliminating 1 valve. We call this demand stream. The reflux drum and column bottoms level must be controlled, requiring two more valves. This leaves us with 2 compositions to be controlled with 2 valves. Traditionally, simple distillation is viewed as 2×2 control problem because remaining 2 composition control loops have strong interactions.
No matter what valves we use for composition control or how we use them, fundamentally there are 2 things that we can manipulate: the feed split and the fractionation. An overall material balance for a column tells us that the distillate flow plus the bottoms flow must equal the feed flow. The feed split is simply the amount of feed that leaves as distillate versus the amount that leaves as the bottoms. Other fundamental manipulative variable is the fractionation which is the amount of separation that occurs /stage. The overall fractionation in a column depends on number of the stages, energy input, and the difficulty of the separation.
Specialized and the Multicomponent Distillation Columns :
We have applied this general procedure to many different types of specialized columns including homogeneous and the heterogeneous azeotropes, the extractive distillation, the strippers and the absorbers and the multicomponent columns. We had also used this procedure for many different column configurations including columns with either liquid or the vapor side draws, columns with the partial condensers and with both packed and tray columns.
Steady State Distillation Models –
Steady state models are easily manipulated and provide the robust solutions. To make change to solution conditions, A few changes need to be made to model input file. The model input file is then submitted to the software which finds new solution. Normally very little time is spent getting converged solutions, which allows us to the efficiently generate large number of case studies necessary for design procedure.
Q1:Write down the design procedure?
Ans: DESIGN PROCEDURE
We have extended the design procedure reported by Tolliver and McCune (1978). The design procedure is composed of the following steps:
Step 1 Develop design basis
Step 2 Select a candidate control scheme.
Step 3 Open loop test using model to find a candidate temperature sensor location.
Step 4 Closed loop test candidate control scheme for feed rate and feed composition disturbances.
Step 5 Objectives met?
We have included a Step 5 to illustrate that the procedure may be iterative. If objectives are met, then procedure is complete. we might return to Step 2 and select a different candidate control scheme or we might return to Step 3 and select a different candidate sensor location. Step we return to tdepends on nature of problem.
Q2: What is the value of Feed rate?
Ans: Feed Rate: 4 to 26 Kpph .
Q3:What is feed composition ?
Ans: Feed Composition: 15 to 60% methanol + some salts.
Q4: Write an example of industrial application?
Ans: Methanol-Water Column.
Q5: Explain Open Loop” Test Using Model To Find Candidate Temperature Sensor Location ?
Ans : Test Using Model To Find Candidate Temperature Sensor Location –
The third step of the design procedure involves what we have termed open loop testing. Purpose of the “open loop” testing is to use the steady state model to identify a candidate temperature sensor location for the inferred composition control. This is accomplished with changing the temperature control manipulative variable up and down from base case value. Provides a plot of three steady state runs where temperature is plotted versus tray number .