Measures for practical, qualitative energy efficiency
Eutech consultants Stelios Bikos and Neil Perry offer up a basket of qualitative and quantitative tools which can be used to cut energy costs by up to 30%.Each year, new regulations call for the curbing of harmful effluent and gases. Manufacturing sites are among the main offenders and many are now investigating efficient processes and resource use to keep within regulatory guidelines. One area where significant process improvements can be made is energy. Reduction in beneficial use and losses can lead to compliance with environmental regulations, but also offers business benefits with savings. Through a systematic cost-cutting programme up to 30% of the energy bill can be saved, unlike typical savings of 5% achieved through reductions in raw materials use.
A site survey often brings out simple asset management techniques as beneficial to energy efficiency: specific plant and building surveys, good housekeeping exercises, shop-floor personnel involvement and motivation. Termed as 'low hanging fruits', these qualitative measures constitute low or no cost solutions while often helping uncover difficult processes for further investigation.
Hidden energy costs
A common problem when pursuing higher energy efficiency is true energy loss identification. To improve operations, manufacturers need to identify energy often hidden in activities other than the obvious, for instance raising compressed air for instruments or pneumatic transfer of material, and notably, producing or reworking waste product which has been processed but is unsuitable for sale. General waste minimisation techniques and overall equipment efficiency techniques can help immensely in the latter case.
Qualitative measures are very valuable, especially when capital expenditure must be avoided. If a more rigorous approach is made clearly necessary, quantitative techniques are best employed. These are systematic and able to produce undisputed targets for improvement but need significantly more data of good quality. For example, Pinch Technology techniques rely on typical fluid stream flows and start and end temperatures to work out heat recovery targets and ways to achieve them. Pinch Technology sits comfortably between ad-hoc qualitative techniques and rigorous mathematical techniques, as conceptual and versatile in its application, yet systematic on heat balances and useful particularly where direct inspection of a process cannot produce evidently beneficial solutions.
Optimisation begins with the systematic, quantitative measurement of energy consumption through monitoring and targeting (M&T). Here, the key process quantities are measured systematically to show the energy consumption in all parts of the process/plant/site. The usual objective of targeting of this kind is generally to identify incremental efficiency improvements akin to qualitative measures. Analysis of the data accrued through monitoring, however, can be the firm basis of rigorous optimisation through a process model. Usual constraints, like commercial (e.g. product demand, energy supply tariff structure etc.), technical (e.g. equipment performance, heat and mass balances), operational (e.g. shift pattern, control scenarios) and notably environmental (e.g. consents on greenhouse gases, liquid effluent, specific energy consumption) can all be formulated in the model and be observed.
Once a process model has been successfully written and validated, it can also be used on-line to help predict and anticipate maintenance needs. These can then be streamlined within the operations plans to achieve minimal disruption and improve overall plant performance.
Rigorous mathematical optimisation needs a combination of engineering knowledge and mathematical expertise to formulate a realistic, solvable model and interpret its results.
Energy efficiency, motivated by either environmental concerns, business peformance or a combination of both, must be pursued with the most appropriate tools for each situation.
A survey ensures systematic cover of all energy issues at a plant, though largely qualitatively. Rigorous process optimisation complements a survey and low or no cost solutions, where possible, as it can quantify energy efficiency, even when masked under poor plant services, availability or right-first-time problems. Conceptual tools, like Pinch Technology, can provide a useful intermediate between practical solutions from a survey and mathematically demanding modelling. Finally, a successful energy efficiency programme in a manufacturing organisation will need the firm commitment of senior management to see recommendations from any of the above measures come to fruition.