September 23, 2008

Process Checklist for Energy Saving in Distillation

Distillation operations have been branded as high energy users. An estimate says 3-5% of the total energy used in the United States was for distillation.

Therefore it is necessary for process engineers to have a ready check list for energy saving in distillation columns. In this post we are suggesting a list for process side. This does not include general recommendations for utilities.

Here is the Process Check List.
  1. What is present energy usage per unit of production? Keep electrical energy and mechanical energy separate from heat energy. Keep separate usage of steam at different pressures. Don't forget to include energy used for auxiliaries such as
    instrument air, vacuum pumps or cooling water.

  2. What is present energy usage per unit of production by competitors? If lower usage, why?

  3. Are foremen and operators sufficiently skilled and trained to incorporate energy conservation techniques in their job duties?

  4. Can product purity be lowered, thereby reducing column reflux and reboiler heat duty?

  5. Can column operating pressure be allowed to float with ambient conditions with subsequent reduction in reflux and reboiler heat duty?

  6. When column is operated at production rates below the economic production rate, is reflux flow reduced to maintain same reflux ratio and lower reboiler heat duty?

  7. Can circulation in the main process e.g. in absorber - stripper combination be reduced.

  8. Is feed stream at optimum temperature to maximize separation and reduce column heat duty requirements.

  9. Is location of feed to column at optimum position?

  10. Can column internals be replaced with more efficient design?

  11. Can additional trays be installed in stripping or rectification sections of column to improve separation, thereby reducing heat duty requirements?

  12. Can an impurity be withdrawn from column to improve separation?

  13. Can the technique of pasteurization be used on existing column, thereby eliminating further separation operations?

  14. Is it economically feasible to convert column operation to a heat pump or vapor recompression cycle?

  15. Can control system be updated to automatic control with an economic payout and subsequent savings in energy requirements?

  16. Can steam supply pressure be allowed to float ?

  17. Are exchangers used in heat recovery maximizing the available heat recovery, considering economics? Will additional exchangers or revisions in the flow scheme improve heat recovery?

  18. Has a procedure been developed for deciding when to remove exchangers that are used in heat recovery service for cleaning? Procedure is based upon economics.

  19. Can excess heat from other process units within the plant be used in this process unit?

  20. Is heat being recovered from column pumparounds at the highest temperature level? Are pumparounds at best tray locations for heat recovery and column separation?

  21. If column operates at high overhead temperature, has heat recovery from overhead being maximized by using two stage condensation and cooling?

  22. Can control valves be resized for less rangeability, but still maintain required system control? Benefits are reduced pressure drop and power loss across the new, larger control valve.

  23. a. If production is to be increased by installing another column, can present column be cascaded with new column to save energy?

  24. Can columns in the distillation train be resequenced to improve separation, production and reduce energy usage?

  25. Can a vacuum pump replace a steam ejector at an energy saving and economic benefit?

You can add more if you have done something else.

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