L4- Sizing batch vessels Flashcards
Occupancy
Volume required in each plant item per unit mass of product (m3/kg)
Sizing Methodology
1) Construct recipe and mass balance, select basis
2) Construct resource-task network
3) Calculate occupancy at each stage
4) Draw Gantt chart & find cycle time
5) (If multiproduct- Allow for cleaning time and work out proportion of working year allotted to each product)
6) Estimate number of batches per year of product
7) Divide annual production rate by no. of batches per year -> production of product per batch
8) Production per batch x occupancy = working volume at each stage
9) Select nearest greater standard vessel volume
Cycle time from range of processing stages for each product
Cycle time = max{processing time for each stage of product X}
Number of batches per year calculation (single product)
No. of batches per year = Hours of operation/cycle time
Production of product per batch calculation (single product)
production of product per batch (tonnes) = tonnes a year/no. of batches per year
Volume of vessel calculation
Volume of vessel = Occupancy x prodcution of product X per batch
Then select nearest greater standard size
Utilisation changed for sizing: calculate new cost relative to original design
[New vessel sizes]^n/[old vessel sizes]^n
Power law for scaling vessel costs
[Cost of vessel a/cost of vessel b] = (Capacity of a/b)^n
n = 2/3 for a cylinder
Multiproduct sizing calculation
1) Cycle time for each product
2) Expression for Total time = nA campaigns x campaign time etc
3) Let all products’ batch size initially be X tonnes
4) Expressions for products, i.e. 50XnA = campaign time
5) Substitute and find whole number campaigns, nA.
6) Check total time expression and try get close (i.e. high utilisation but no violation)
7) Take new values for nA etc. and calculate batch size: XA = campaign time / (batches x nA)
8) Find occupancy, vessel volumes and take:
max{each vessel for products} = required volume
