Energy efficiency in the industry - Concepts & realisation

Distribution- and transformation-related losses can be minimised by decentralising the energy supply toward modular and efficient CHP units. Aside from the conservation of the in-house electricity privilege (reduction of the EEG levy on the self-generated and utilised electricity), the high overall efficiency associated with the combined generation of power and heat is the core of this technology. Gas and oil engines are used in most cases. They are driving generators to produce power, while the accumulated waste and cooling heat can be utilised at the same time. Alternatively, it is also possible to use gas turbines, special fuel cell systems or Stirling engines as well as other fuel engineering with subsequent steam turbine or ORC processes. In order to obtain government-sponsored current feed-in within the scope of the KWKG, the goal must always be to satisfy the high-efficiency criterion (total efficiency of >75%).  

In classical physics, the 1st law of thermodynamics is known as law of conservation of energy: Energy cannot be generated and disappear out of nowhere. Energy can only be transformed from one form into another form. An additional thermodynamic parameter is used in the 2nd law, which is entropy. Thus, any spontaneous reaction leads to an increase of the latter, whereby it is also possible to define the technical usability of a form of energy by means of entropy. In so doing, anergy is the part of a form of energy that can no longer be technically used; in contrast, exergy is the useful part of it. 

Accordingly, heat is not equal to heat; the temperature level essentially determines the ratio of exergy and hence the quality of the heat. Within the scope of exergetic optimisation, potentials can thus be harnessed, which usually remain idle in large steam networks of companies. In so doing, pressure reducing stations usually serve the connection of high, medium and low pressure networks or individual steam distributors are supplied with a higher pressure/temperature level by way of regulating valves. Indeed, the energy is conserved in these locations, but part of the exergy is transformed into anergy unused. 

This potential can be utilised for the provision of technical work and electric power can for example be substituted when using microturbines or displacement machines instead of regulating valves.

The exploitation of waste heat can make a significant contribution to the effective utilisation of energy sources and hence to saving energy in the industry. In industrial processes, a considerable part of the expended energy often does not remain in the product, but is instead released into the environment in the form of heat. Reintegrating this heat back into the process is often associated with major technical efforts. An effort that is well worth it! 

On the overall balance of an energy generation system, the majority of costs over the course of the lifetime or contract period are incurred by fuel acquisition. Meanwhile, the capacity cost of the investment is a relatively small component. No fuel acquisition costs are incurred for waste heat recovery technologies. Correspondingly, the benefit, i.e. the recovered energy or the substitution of primary or secondary energy, is only offset by the capacity cost of the investment. In many cases, this justifies enormous equipment-based expenditures. 

Besides the waste heat source and hence the type of heat transfer media, which are usually highly contaminated combustion, ventilation or drying gases as well as waste water, waste lyes or even hot solid matter, it is mainly the often low temperature of the waste heat that is problematic.

From an energetic point of view, it should always be checked first whether there is a need for heat of this temperature anywhere in the production, e.g. if there are any process or space heating needs. If this is not the case, different technologies are available for the high-loss transformation of waste heat into electric power, into heat with a higher temperature, into cooling or for use in district heating networks, depending on the performance and temperature level.

The exploitation of low-temperature heat is one of the greatest potentials for sustainable energy resources management. Depending on the balance scope, heat is always the end of every energy transformation chain. 

In so doing, the temperature level is not a direct predictor of the amount of energy, but only of the quality of the heat. Huge amounts of energy are released into the environment every day by companies and industries in the form of heat at temperatures ranging between 40 and 90 °C. 

If we succeed in exploiting this type of heat at least partially, energy conservation can be realised in large quantities and in a broad spectrum.

Heat transformation

Many drying, evaporation and distillation processes, especially in the food and paper industry, require large amounts of heat at a temperature level of about 100-120 °C, while at the same time generating large quantities of waste heat in the range of 80 to 90 °C.

GETEC is currently pursuing a promising technological approach aimed at increasing the temperature of waste heat by about 20-40 K, which is precisely harnessing the potentials mentioned above. Unlike with conventional heat pumps, no additional secondary energy (e.g. electric power) is used in this process, but the operating energy in fact originates from the waste heat itself. In so doing, nearly 50% of the recovered waste heat is raised to a higher temperature level. The temperature level of the remaining waste heat is lowered by about the same amount.

Absorption chiller with low-temperature heat  

Cooling is of vital importance in the modern industrial society. Particularly the food and beverage industry is consuming a large share of primary energy for cooling. In this context, a distinction is made between

• climatic cooling (approx. 6/12 °C),
• process cooling with temperature levels of approx. 0 °C or – 10 °C and
• intense cooling with temperatures below – 30 °C,

since different refrigerating agents and technological methods are used for the generation, depending on the temperature level of the cooling. 

Cooling is generated mainly by means of compression refrigeration systems, as the investment and space requirements for them are low. Their poor thermodynamic effectiveness is undoubtedly a disadvantage, because compression refrigeration machines consume electric energy as operating power, which is provided with a COP (Coefficient of Performance, ratio of usable refrigeration to spent electrical power) value of 1.5 to 5 – depending on the temperature level – in addition to the high internal losses.

The energetic and climatic challenges of our time require us to focus on a high energetic effectiveness of the transformation and use, the efficient recovery of waste heat and the avoidance of refrigerants with a high GWP (Global Warming Potential). The waste heat recovery and associated substitution of high-quality electric energy is an indispensable contribution to an efficient energy transformation and exploitation.

The development of a novel absorption refrigeration machine is another approach pursued by GETEC. It is designed to help companies requiring process cooling to considerably increase their energy productivity. The goal is to utilise mainly the heat potentials and/or waste heat underused in the past, with an approximate temperature level of 80°C (e.g. from the combined heat and power generation) for the provision of process cooling at a temperature level of up to -10 °C. In this regard, new ground is broken in the field of working materials systems and a knowledge application gap bridged in the field of absorption refrigeration.

A substantial portion of the total energy consumption is generated by the driving of:

• Pumps
• fans
• air compressors
• compression cooling machines
• belt conveyors

In so doing, the greatest energy savings potential can be attained with the often oversized pumps and fans. An electronic drive control by means of frequency converters (FCs) can achieve a formidable increase in efficiency. In the past, drives were initially produced with larger sizes because of the lower investment costs, and a mechanical or hydraulic throttle or control was implemented during the operation. In these cases, 30% of the electrical power requirement can be reduced on average by removing the throttle and implementing a control by means of frequency converters. With today’s electricity rates and investment costs for FCs, this measure often pays for itself after just a few years. 

In any case, replacing old drives with new motors boosts the energy efficiency. The economic benefit is relatively small and is highly dependent on the energy rate. If old motors are not capable to be operated with FCs, replacing them with a new motor makes sense in any case. 

According to the German Energy Agency (dena), the sale of motors with a relatively low efficiency has been restricted since the middle of 2011. Accordingly, motors have been divided into efficiency classes, with the following regulation in effect globally since 2009:

Energy efficiency classes of electric motors in effect since 2009:

Aside from saving electric power, it is also possible to recover heat with modern compressors including drives and their control within the provision of compressed air. In so doing, several sources can be harnessed, e.g. the waste heat of the drives, the heated refrigerant/lubricant and the heat absorbed by the environment in connection with the expansion, which is released again during the compression. 

All in all, up to 96% of the supplied electric driving power can be harnessed, provided that there is a need for low-temperature heat, such as e.g. room heating.

The requirements are high for lighting concepts of modern workplaces. Not only the optimal illumination and adequate brightness are essential, but the colour reproduction is also vital, depending on the task.

"In Germany, the basic lighting requirements with regard to the safety and health at the workplace are governed in the Workplace Ordinance (ArbStättV). The ArbStättV is applicable to all workplaces. The general lighting requirements set forth in the ArbStättV are specified in more detail in the Technical Rules for Workplaces ASR A3.4 "Lighting". Additional industry-specific information regarding the topic "Lighting" can be found in the brochures issued by the accident insurers. The accident prevention regulation "Principles of Prevention" (BGV [Regulations of the Professional Association] A1 and GUV [Statutory Accident Insurance] V A1) refers to the ArbStättV and is additionally applicable to individuals with voluntary insurance coverage. The generally accepted engineering practice represented in DIN EN 12464-1 in Germany must be observed when planning the lighting layout in consultation with the employers." The above is an excerpt from the guide to DIN EN 12464/1 issued by the Association for the Promotion of Adequate Lighting.

In addition, the lighting design and the selection of lamps are determined by economic factors, both for new lighting as well as upgrades of an existing lighting system.  Depending on the required economic payback period of upgrades or the planning/balancing period of the concept development, both the energy efficiency of lamps as well as the incorporation of time and motion switches play a role. In addition, a complex light control system can be used, which also controls the daylight- and zone-dependent light intensity aside from production- and vacation-related influences.

Based on experience, the energy efficiency of the entire lighting system can be improved by more than 60%, when the lighting requirements of the respective workplace outlined above are taken into account.

In addition to the energy efficiency, the service life and maintenance costs of the lamps or luminaires also have a significant impact on the economic rating of the lighting system. This currently leads to a growing use of LED technology, thanks in large part to its favourable score in terms of maintenance costs and long operating times.