Complex manufacturing operations involve transporting and heating raw materials to the temperature of reaction, separation of the products and byproducts, converting to final products, and recovery of the waste byproducts and waste heat to the extent economically feasible. Over time the race for higher production rates and capacity, more complex product slates, greater emission and effluent constraints, and restrictions on maintenance has outrun the ability of the plant to optimize its energy and fuel usage. Vendors promise that by implementing their software platforms, you can get the optimization desired via proper tracking of energy coupled with pricing information of each energy stream. Unfortunately, this may work well for an existing building with HVAC requirements or a simple industrial process, but is inadequate for industrial systems. Plants that are old and complex, have been changed significantly, over or under designed, and built at a time when energy and water use were less at a premium than they are today have need for energy efficiency fundamental work. In these cases it makes more sense to spend limited resources on a more comprehensive approach.
The first step to solving this dilemma is not found in sophisticated energy control software, but in starting with the basics - steam and water balances that are developed under typical conditions in various seasons. These balances are built from good process flow diagrams coupled with instrumentation which take accurate and representative measurements of steam and water properties and flows. With a robust and easy to follow model, the balances become the basis for understanding where there are opportunities for saving energy through using recovered heat rather than primary steam or thermal fluid. This then allows for either lower fuel use or increased power generation. A good set of balances can be developed using an existing data acquisition system as long as the sensors have been calibrated and are measuring the required information. If not, new sensors and transmitters must be added to the system and old ones must be calibrated or replaced.
The model results further allow for benchmarking against similar plants, in terms of energy, raw material and water usage per unit of product produced. The use of a model based on good balances can nail down where there are gaps with a benchmark and lead to solutions which involve a number of acceptable and practical methods. It is at this point that discussions with the plant stakeholders - operators, engineers, and leadership is undertaken. While, the best available technology may not be economically feasible, it is likely that lower capital improvement changes with high ROI's will be identified. These include additional heat exchangers which can utilize lower temperature water, insulated tanks which keep varied temperature streams segregated, flash tanks where they are not being fully utilized, condensate return issues, desuperheater and steam trap issues, and repiping of higher temperature water flows to take advantage of this heat in processes that can benefit from them directly. These projects when implemented will reduce operating costs and increase the plant's viability and profitability. Plant staff need to be fully involved to insure that recommendations are practical and will not impact the process adversely.
On the power side, the model results will show how much steam can be saved through appropriate projects, and how this steam translates into power generation. Additionally important are uses of power that could be reduced or eliminated by reducing recycling of water, resizing of pump impellers, and selective implementation of variable frequency drives. Again, buy- in with the plant staff needs to be made before moving further on recommendations. The result of reducing demand and increasing generation will result in a net power sales increase.
The cost for this activity is as you might expect a great deal less than software optimization platforms with supervisory control packages, and it is not a recurring cost. The important difference though is that it will result in projects that have high ROIs and are proven to be effective by benchmark plants, model results, and operating data. Once the plant staff have put these projects in place and the full plant has been sufficiently updated and made efficient, then it may be time to consider optimization software and controls.
The return from this approach is significantly greater than could be achieved from typical software based systems. It has been estimated by various vendors that their energy management software systems will save 1-3% of energy per year. The approach elucidated here will save 5-20% of energy use since it will involve structural changes that will make the process and all energy related aspects more efficient. The savings will be locked in as they are engineering changes which cannot be easily undone by operations staff who may have opposing motivations.
While great software and controls are the ultimate answer to making manufacturing optimized and automated, the first steps of a detailed process flow diagram and energy balance are still both necessary and sufficient to make significant progress in reducing a manufacturing plant's energy and water footprint. These foundation blocks are critical to seeing sustainable and real energy and process efficiency.