Refinery Optimization: How to Run an Oil Refinery


PROC OPTMODEL Statements and Output

The NOMISS option in the first READ DATA statement ensures that only nonmissing values of the variable multiplier in the arc_data data set populate the arc_mult parameter. Because arc_mult is declared with an initial value of 1, parameters with no value default to 1.

proc optmodel;
   set <str,str> ARCS;
   num arc_mult {ARCS} init 1;
   read data arc_data nomiss into ARCS=[i j] arc_mult=multiplier;
   var Flow {ARCS} >= 0;

   set <str> FINAL_PRODUCTS;
   num profit {FINAL_PRODUCTS};
   read data final_product_data into FINAL_PRODUCTS=[product] profit;

The following FOR loop converts profit from pence per barrel to pounds per barrel, without altering the input data set:

   for {product in FINAL_PRODUCTS} profit[product] = profit[product] / 100;

Most arcs appear in the arc_data data set, but the following assignment statement uses the set operators UNION and CROSS to augment the ARCS set with an arc from each final product to the sink node:


   ARCS = ARCS union (FINAL_PRODUCTS cross {'sink'});

   set NODES = union {<i,j> in ARCS} {i,j};

   max TotalProfit = sum {i in FINAL_PRODUCTS} profit[i] * Flow[i,'sink'];

   con Flow_balance {i in NODES diff {'source','sink'}}:
      sum {<(i),j> in ARCS} Flow[i,j]
         = sum {<j,(i)> in ARCS} arc_mult[j,i] * Flow[j,i];

   set <str> CRUDES;
   var CrudeDistilled {CRUDES} >= 0;

Because the decision variable CrudeDistilled automatically contains the .ub suffix, you can populate CrudeDistilled.ub directly by using the following READ DATA statement, without having to declare an additional parameter to store this upper bound:


   read data crude_data into CRUDES=[crude] CrudeDistilled.ub=crude_ub;
   con Distillation {<i,j> in ARCS: i in CRUDES}:
      Flow[i,j] = CrudeDistilled[i];

The SETOF operator, used together with the concatenation operator ($||$) in the following statements, enables you to create one index set from another:


   set OILS = {'light_oil','heavy_oil'};
   set CRACKED_OILS = setof {i in OILS} i||'_cracked';
   var OilCracked {CRACKED_OILS} >= 0;
   con Cracking {<i,j> in ARCS: i in CRACKED_OILS}:
      Flow[i,j] = OilCracked[i];

   num octane {NODES} init .;
   read data octane_data nomiss into [i] octane;

   set <str> PETROLS;
   num octane_lb {PETROLS};
   read data petrol_data into PETROLS=[petrol] octane_lb;

   num vapour_pressure {NODES} init .;
   read data vapour_pressure_data nomiss into [oil] vapour_pressure;

As expressed on , both octane numbers and vapour pressures of the blended fuels are ratios of linear functions of the decision variables. To increase algorithmic performance and reliability, the following two CON statements linearize the nonlinear ratio constraints by clearing the denominators:

   con Blending_petrol {petrol in PETROLS}:
      sum {<i,(petrol)> in ARCS}
         octane[i] * arc_mult[i,petrol] * Flow[i,petrol]
   >= octane_lb[petrol] *
      sum {<i,(petrol)> in ARCS} arc_mult[i,petrol] * Flow[i,petrol];

   con Blending_jet_fuel:
      sum {<i,'jet_fuel'> in ARCS}
         vapour_pressure[i] * arc_mult[i,'jet_fuel'] * Flow[i,'jet_fuel']
   <= &vapour_pressure_ub *
      sum {<i,'jet_fuel'> in ARCS} arc_mult[i,'jet_fuel'] * Flow[i,'jet_fuel'];

Similarly, the following CON statement linearizes the fuel oil ratio constraints by clearing the denominators:

   num fuel_oil_coefficient {NODES} init 0;
   read data fuel_oil_ratio_data nomiss into [oil]
      fuel_oil_coefficient=coefficient;
   num sum_fuel_oil_coefficient
      = sum {<i,'fuel_oil'> in ARCS} fuel_oil_coefficient[i];
   con Blending_fuel_oil {<i,'fuel_oil'> in ARCS}:
      sum_fuel_oil_coefficient * Flow[i,'fuel_oil']
   = fuel_oil_coefficient[i] * sum {<j,'fuel_oil'> in ARCS} Flow[j,'fuel_oil'];

   con Crude_total_ub_con:
      sum {i in CRUDES} CrudeDistilled[i] <= &crude_total_ub;

The following CON statement uses the SAS function INDEX together with the colon operator (:) to select the subset of arcs whose tail node contains ‘naphtha’ in its name:

   con Naphtha_ub_con:
      sum {<i,'reformed_gasoline'> in ARCS: index(i,'naphtha') > 0}
         Flow[i,'reformed_gasoline']
   <= &naphtha_ub;

   con Cracked_oil_ub_con:
      sum {<i,'cracked_oil'> in ARCS} Flow[i,'cracked_oil'] <= &cracked_oil_ub;

   con Lube_oil_range_con:
      &lube_oil_lb <= Flow['lube_oil','sink'] <= &lube_oil_ub;

As expressed on , the premium ratio constraint involves a ratio of linear functions of the decision variables. The following CON statement linearizes the nonlinear ratio constraint by clearing the denominator:

   con Premium_ratio_con:
      sum {<'premium_petrol',j> in ARCS} Flow['premium_petrol',j]
   >= &premium_ratio *
      sum {<'regular_petrol',j> in ARCS} Flow['regular_petrol',j];

   num octane_sol {petrol in PETROLS} =
      (sum {<i,(petrol)> in ARCS}
         octane[i] * arc_mult[i,petrol] * Flow[i,petrol].sol) /
      (sum {<i,(petrol)> in ARCS} arc_mult[i,petrol] * Flow[i,petrol].sol);

   num vapour_pressure_sol =
      (sum {<i,'jet_fuel'> in ARCS} vapour_pressure[i] *
         arc_mult[i,'jet_fuel'] * Flow[i,'jet_fuel'].sol)
      / (sum {<i,'jet_fuel'> in ARCS} arc_mult[i,'jet_fuel'] *
         Flow[i,'jet_fuel'].sol);

   num fuel_oil_ratio_sol {<i,'fuel_oil'> in ARCS} =
      (arc_mult[i,'fuel_oil'] * Flow[i,'fuel_oil'].sol) /
      (sum {<j,'fuel_oil'> in ARCS} arc_mult[j,'fuel_oil'] *
         Flow[j,'fuel_oil'].sol);

   solve;
   print CrudeDistilled;
   print OilCracked Flow;
   print octane_sol octane_lb;

Although the previous PRINT statements print all values of the given parameters, the following two PRINT statements use an index set to print a specified subset of the values:

   print {<i,'jet_fuel'> in ARCS} vapour_pressure vapour_pressure_sol;
   print {<i,'fuel_oil'> in ARCS} fuel_oil_coefficient fuel_oil_ratio_sol;
   create data sol_data1 from [i j] Flow;
quit;

Figure 6.2 shows the output from the linear programming solver. For this test instance, it turns out that the optimal solution contains no fuel oil.

Figure 6.2: Output from Linear Programming Solver

The OPTMODEL Procedure

Problem Summary
Objective Sense Maximization
Objective Function TotalProfit
Objective Type Linear
   
Number of Variables 51
Bounded Above 0
Bounded Below 49
Bounded Below and Above 2
Free 0
Fixed 0
   
Number of Constraints 46
Linear LE (<=) 4
Linear EQ (=) 38
Linear GE (>=) 3
Linear Range 1
   
Constraint Coefficients 158

Performance Information
Execution Mode Single-Machine
Number of Threads 1

Solution Summary
Solver LP
Algorithm Dual Simplex
Objective Function TotalProfit
Solution Status Optimal
Objective Value 211365.13477
   
Primal Infeasibility 4.479261E-11
Dual Infeasibility 6.217249E-15
Bound Infeasibility 0
   
Iterations 22
Presolve Time 0.00
Solution Time 0.00

[1] CrudeDistilled
crude1 15000
crude2 30000

[1] OilCracked
heavy_oil_cracked 3800
light_oil_cracked 4200

[1] [2] Flow
cracked_gasoline premium_petrol 1546.79
cracked_gasoline regular_petrol 389.21
cracked_oil fuel_oil 0.00
cracked_oil jet_fuel 5706.00
crude1 heavy_naphtha 15000.00
crude1 heavy_oil 15000.00
crude1 light_naphtha 15000.00
crude1 light_oil 15000.00
crude1 medium_naphtha 15000.00
crude1 residuum 15000.00
crude2 heavy_naphtha 30000.00
crude2 heavy_oil 30000.00
crude2 light_naphtha 30000.00
crude2 light_oil 30000.00
crude2 medium_naphtha 30000.00
crude2 residuum 30000.00
fuel_oil sink 0.00
heavy_naphtha premium_petrol 2837.90
heavy_naphtha reformed_gasoline 5406.86
heavy_naphtha regular_petrol 155.24
heavy_oil fuel_oil 0.00
heavy_oil heavy_oil_cracked 3800.00
heavy_oil jet_fuel 4900.00
heavy_oil_cracked cracked_gasoline 3800.00
heavy_oil_cracked cracked_oil 3800.00
jet_fuel sink 15156.00
light_naphtha premium_petrol 0.00
light_naphtha reformed_gasoline 0.00
light_naphtha regular_petrol 6000.00
light_oil fuel_oil 0.00
light_oil jet_fuel 0.00
light_oil light_oil_cracked 4200.00
light_oil_cracked cracked_gasoline 4200.00
light_oil_cracked cracked_oil 4200.00
lube_oil sink 500.00
medium_naphtha premium_petrol 0.00
medium_naphtha reformed_gasoline 0.00
medium_naphtha regular_petrol 10500.00
premium_petrol sink 6817.78
reformed_gasoline premium_petrol 2433.09
reformed_gasoline regular_petrol 0.00
regular_petrol sink 17044.45
residuum fuel_oil 0.00
residuum jet_fuel 4550.00
residuum lube_oil 1000.00
source crude1 15000.00
source crude2 30000.00

[1] octane_sol octane_lb
premium_petrol 94 94
regular_petrol 84 84

[1] vapour_pressure
cracked_oil 1.50
heavy_oil 0.60
light_oil 1.00
residuum 0.05

vapour_pressure_sol
0.77372

[1] fuel_oil_coefficient fuel_oil_ratio_sol
cracked_oil 4 .
heavy_oil 3 .
light_oil 10 .
residuum 1 .