Numerous cost reduction programmes have been launched by production executives to restrict the financial pressure from competitors in the Far East and meet the increased costs for energy and raw materials. In the meantime, most of these continuous improvements have already been implemented. New savings potentials can only be identified with the help of engineering partners who systematically analyse the complete facility for possible economies and simultaneously develop concepts for transforming their ideas into cost reductions.
Dr. Hans-Hubert Hildenbrand
The year 2008 was hit by an unprecedented rise in energy costs. Throughout the nineties, the price of crude oil remained relatively stable at an average of between 12 and 20 US$/barrel but took a noticeable upward turn from 2001 onwards. An intermittent peak was reached in 2007, in which an average price of 69.10 US$/barrel was recorded. In the middle of 2008, this figure shot up to the previously unimaginable level of 140 US$ prior to falling again to below 60 US$ in the last few months of the year. The same trend can also be discerned – though with a slightly delayed effect – for natural gas. Only electricity prices experienced a downward trend in the mid- nineties due to the deregulation of the electricity market. However, the industry has since reverted to its customary increases. Not many production companies can actually pass on this cost increase to their clients. Providing costs and margins do not get out of control as a result, concepts to rationalise the use of energy are in considerable demand. On the one hand, they facilitate the desired reduction in production costs while on the other, they help protect the environment and natural resources. Engineers in InfraServ Gendorf’s Business Unit Engineering have pooled their expert know-how – the outcome of planning industrial plants for, and consultancy services to, medium-sized enterprises – in a project to optimise energy efficiency.
Analysis of the actual situation
The basis for a successful energy study is always a detailed analysis of the actual situation. All energy-related plant data is initially collected and systemised. The relevant process information relates to primary thermodynamic state parameters like pressure and temperature. Caloric data such as specific heat capacity or reaction, vaporisation, sublimation and condensation enthalpies must also be collected at this stage of the investigation. Finally, the mass and volume flows of the materials processed in the plant have to be determined. In the next step, all relevant data must be allocated to the process. The engineering partner’s deep understanding of the process in question is an essential precondition of finding and evaluating suitable energy savings potentials. Specialists in the inspected plant’s operation are required to visualise the process and assign the process data – because only they can provide the necessary details.
After completing the analysis of the actual situation and summarising the received data and facts in a short process description, the plant’s energy balance can be drawn up. A basic knowledge of thermodynamics is needed to prepare the balance and calculate the energy budget. Reactions and phase transitions must be included in addition to classic enthalpy calculations for the sake of precision. The accuracy of the balance should be between 10 and 20 %, depending on the complexity of the actual analysis. The more detailed the data evaluation for the analysis, the more precise the study will be. Along with an evaluation of the energy budget, the balance additionally serves to verify the determined process data. If it appears to be too inaccurate, the data concerned must be critically reviewed and confirmed or updated with measurements as appropriate. Unfortunately, no plant can afford the number of measurements required for a complete balance. Part processes may have to be modelled by means of simulations to ensure that the balance remains significant. Extensive experience in procedural calculations and process planning/engineering is crucial, in order to check the results of the process simulations for plausibility and consistency. The results of the balance in the form of classic lists and schedules are also integrated in base flow charts, in which the actual data and the resulting enthalpies are entered.
The energy flow of the units can be visualised using a Sankey diagram, in which the enthalpy sizes in relation to one another are shown as bars with a variable thickness. An energy consumption analysis should be performed parallel to the balance. It shows the main energy consumers, making it easier to focus on those plant components where the greatest savings can be achieved due to the high energy conversion.
Potential analysis
The purpose of the energy study is to reveal potential energy economies. On the one hand, technical know-how spanning all engineering disciplines is a must; on the other hand, experience in handling energy is vital to ensure that at the end of the process, the savings potentials described are actually reliable. One valuable source of ideas that should always be tapped is the operating personnel, who know the special features of the plant better than anyone else and also have an instinct for practicable measures. Checklists are likewise helpful and can serve as a starting point for suggestions. Infaserv Gendorf’s BU Engineering uses such lists based on the results of previous energy audits for this purpose. The checklists cover chemical, electrical, process control and civil engineering. They are continuously updated and consequently reflect the most recent knowledge available.
Together with a graph or table of the plant’s energy budget, the ideas derived in this way provide Infraserv Gendorf’s engineers with useful inspiration for optimising energy utilisation. No technical discipline is overlooked – in addition to classic heat displacement, pinch analyses, more efficient motors and demand based control strat-egies for drives, the aspects such as the latest state of the art in technology, alternative operating concepts and ways to optimise established processes are also comprehensively examined. The resulting set of ideas shows possible reductions, taking account of the specific energy prices. As an environmental side-effect, the energy savings can also be declared as a CO2 reduction, which from today’s point of view is just as important as lower energy consumption.
As mentioned earlier, only a very few of these savings are achievable without capital investments. The necessary funds must be assessed in a second step for this reason. Since it is not possible to initiate a separate project plan and investment calculation for every single idea, a technique must be found for estimating capital investments quickly and easily, yet nevertheless with the required accuracy. Infraserv Gendorf has vast experience in plant engineering projects, so that sufficiently precise cost estimates can be drawn up to underlie further decisions about plant operation.
The savings and investments calculated in an energy study of this kind have a tolerance of approximately ±25 % and are hence within the acceptable limit for a feasibility study.
Prior to implementing the identified savings and investments, each savings idea should be validated. The simplest benchmark is to determine the return on investment. If the payback time is within the target set by plant operations, the idea should be considered in more depth – as a general rule, this refers to classic basic and detailed engineering. If this period is marginally exceeded, the potential should be re-evaluated after a while and compared to the actual energy costs. If the investment is not recuperated for considerably longer than the defined time, the savings idea should be noted but not further contemplated.
A new discussion with operating personnel is called for at this stage at the latest. The savings potentials identified so far have only been investigated from the energy perspective. These ideas must now be aligned with the needs of the production process. The operators must assess whether the formulated suggestions, which could have a significant impact on the process, are feasible from the point of view of plant duty. This last step may necessitate still finer adjustments to both savings and investments but is mandatory for later realisation.
Energy studies carried out in medium-sized enterprises and at the production facilities of major chemical companies in accordance with the concepts described above confirm that commercially significant energy savings equivalent to up to 15 % of annual consumption can be realised. However, this success rate depends on the plant type and on the energy savings measures already in place. Nevertheless, the experience of Infraserv Gendorf’s BU Engineering shows that every plant holds considerable latent potential in this area that is simply waiting to be tapped. Providing they are conducted professionally, energy studies can make a valuable contribution to safeguarding the competitiveness of plants, manufacturing sites and production capacities.
Hall 9.1, Booth E20
Online-Info www.cpp-net.com/2209401
Share:
