April 01, 2008

Energy: Why important for Process Engineers

Fuel for energy is generated by the nature. For example, C1 (carbon in the form of CO2) is naturally synthesizes (photosynthesis in presence of natural UV radiation) to molecule Cn (like starch, sugar or cellulose), which are used directly /or indirectly as fuel/ or feed stocks for fuel generation. Consumption of available fuels higher than generation is creating not only fuel shortage but also leaving behind bad consequences to the environment due to exhausted excess carbon dioxide.

Being desired transformations can’t be avoided in the process industries, higher energy wastages in them demands higher input energy. How energy is wasted in the process industry? To understand it, consider following cases:

  1. Doing more, thus wasting more

  2. Doing more, but using less

  3. Wasting more, thus doing more

Doing more, thus wasting more
For example, pump filling overhead constant level tank at higher flow rate than required, thus subsequently overflowing excess amount of liquid to ground tank. Being pump is operating at much higher capacity than required, excess energy is wasted.

Doing more, but using less
For example, use of higher capacity conveyor for small amount of material transportation. Underutilization of material conveyor wastes more energy for unit production rate.

Wasting more, thus doing more
For example, high number of pipe fittings used in the pipe routing leads to high fluid energy wastage in terms of frictional pressure drop, thus more work is to be done by the pump.

Right amount of energy for desired transformations is the ultimate aim of energy conservation. Reduction in energy wastage to minimum reduces the energy demands in the process plants. Following steps for energy conservations are discussed here:

  1. Good Housekeeping

  2. Optimization of Plant Operation

  3. Hardware Modification or Replacement

  4. Process Modification

Good Housekeeping
This is foremost simple step, which any process industry can easily adopt. Arresting steam leakages, stopping idle operating pumps or mixing agitators, etc. are the typical examples falls under this category. Being the simple steps, it absolutely doesn’t require any financial investment and can be implemented at any time. It requires only the energy conscious culture in the process industry. This step itself can save ~5% in energy bills of the industry.

Simply organizations need culture where everyone from shop floor to top management feels himself involved in the process.

Optimization of Plant Operation
Excess capacity, provided by the plant designer as safety margin, of the plant hardware provides the scope of using it during actual plant operation. Thus, process plant hardware need to be tuned for energy efficient operation. Liquid transportation with maximum flow capacity of the pump, minimizing reflux ratio for distillation column, etc. are the well known examples for process plant optimization. The optimization exercise require either no or minor financial investment. Though some operational time may be consumed for setting rightful optimum parameters, but often results attained are very positive as far as energy saving is concerned.

Hardware Modification or Replacement
Reduced efficiency of existing hardware e.g. scaled or blocked heat exchanger tubes, entry of innovative energy efficient devices in the market like high efficiency distillation column packing, poor selection of hardware at the time of first purchase e.g. lower pipeline size, etc. demands much higher input energy than actually required for desired transformation. Necessary hardware modification or replacement conserves energy in the process plant. Unlike previous two categories, it requires low to medium level financial investment along with process plant stoppage for changeover of the troubling hardware.

Process Modification
Many times overall or part of the process is modified for the sake of overall energy savings. Process routes as well as transformation steps are altered to minimize input energy supplies. It requires extensive studies at various levels starting from paperwork to laboratory, pilot plant & semi-commercial levels. Usually such process modifications require high investments as well as higher implementation time for gaining energy benefits. But they are essential at a stage when business need improvement due to tough market competition.

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