Use of Profit Equations to Select Control Applications
Publication Date: 2012-Jun-07
The IP.com Prior Art Database
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IL'I'LE: : USE P:IOFIT EQUATIONS TO SELECT ADVANCED CONTROL APPLICATIONS
Generally before undertaking any advancea control project
i t is necessaiy to identify the useful controls to be implemented. Sometimes thi can be misleading or require change as the project continues. i pecially now, as profit values arc constantly shifting in highly vol-tilemarkets. For instance : Implementingconversion control on a train of ethylene furnaces can be very tricky. Individual fcinace coke conditions and coking rates, along with changing $rocii--ctvalues and feedstock rates reqLire constant re-evaluation of targets. In such case, the advanced controls require re-ev.luatlon almost continuously.
Itwouldappear then, that the selection of the control application is best at the process level. Here profit parameters can be constar,tlyanalyzed with on-line data and the optimum app- lication can te selected on a "Real-Time"basis.
This a:ticle presents an example that uses on-line profit analysis to select the control applications.
The prclfit equation - The profit equation is familiar to
most process <ngineers. It is used extensively in LP programs and ;,r~cesssurve}'s to determine optimum operating conditions such as: Yeedrates, cor.versiontargets, etc. Similiarly it can be used to select and identify advanced control applications. For this purpose.
' i i ~ c . profit eytiation is useful in that it :
The last factor is important when selectin9 advanced controls,
III that the il,pact
on the plant profitability should be known for each application. Certainly in lieu of changing profit values. In some cases for example, an application may not be profitable
0 i f left on-line.
Developing the profit equation for a process plant and using it can varjy in difficulty. In general, the more streams and inter- 1-actions
the mc re complex the profit equation. Nevertheless, the
. procedures in.olvedare the same. These are :
Step 1) Generate the elements of the profit equation from
material and energy balances. Assemble them into b ' ' ~ ~ 7 \
the profit equation form. That is : '
t" 7 0 Lr
Profit = LProd - feed - roper ( E q . 1 ) 3
Step 2 Substitute known relationships ot manipulated vartables into the elements of the profit equatlon. These are usually obtained from plant tests, lab analysis, technical data, etc.
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ztcp > , Optirrrzc the profit equation wit" respect to the xanipulated variables using numciical methods.
S C c p 4 Analyze each element of the profit equation for potential applications (ie: Select application, modify control target, etc..)
The prcfit equation can be used at the beqinning of a Control pr~jectto idintify the useful control applications. Later, it can
st updated (0.a p~riodicbasis) and used tu sei+'ct specific applica- tions or chanc,e operating targets. In addition, it can be used to determine the relative success of an applicatior.by comparing profit v a l u e s without application versus values with ap...