Heat recovery for pneumatic transport
Making waste heat usable for processes
Companies attach more and more importance to the energy optimisation of their production. They are scrutinising their technical plants and processes. The objective: reducing costs and increasing the sustainability of operations through more rational use of resources. Operators with high energy consumption have a particularly effective lever for greater efficiency.
Making waste heat usable for processes
In addition to smart plant control and the use of highly efficient compressors and blowers, focus is placed on heat recovery systems. A considerable share of energy used for compressed air generation is naturally converted into heat. However, companies can recover large quantities of heat energy from air for further use with only low capital investments. Food companies use heat for heating and hot water preparation, but also immediately for production.
You can achieve maximum efficiency increases by implementing a comprehensive heat concept for your compressed air plant with the solutions from AERZEN. This works for new plants, but can also be realised for existing systems with only minimal effort and expenditure.
Compressed air generation heat development unavoidable
Energy efficiency is decisive for the profitability of compressed air generators. The process air specialist AERZEN masters this challenge with an efficient consulting and service range, guaranteeing the economical operation of its products over their entire life cycle. Measures to increase efficiency in process air explore diverse potential. They are geared towards optimised energy use for compression, the reduction of pressure losses and the use of economical maintenance concepts. Smart systems also play an important role in the continuous monitoring of plant performance. Nevertheless, heat recovery still offers the greatest potential for increasing efficiency – by far.
Heat sources in the compression of process air
A considerable part of energy used at the compressor stage is converted into thermal energy. The compression of air generates very high temperatures on the discharge side – reaching temperatures of up to 280°C when a screw compressor is used, for example. Without heat recovery, fans discharge the unnecessary heat into the surroundings. A portion of the energy also passes from the process air through the pipe system to the surroundings.
Depending on the plant, you, as the operator, can recover up to 85% of this valuable energy and open up a range of other operational applications for it. The transfer of heat from the air to the conveying medium, water, ensures the necessary flexibility. This is realised by special heat exchangers, directly downstream from the compressor stage in the process air circuit. They cool down the air and transfer the heat to the conveying medium, water. A lower share of used energy accumulates under the compressor’s acoustic hood, in the form of heat. The motor, silencer and compressor emit heat from friction losses, for example, into the air. The exhaust air reaches temperatures between 30 and 60°C. It can be used without further conversion to heat nearby office premises or production areas. To this end, AERZEN equips its blowers and compressors with exhaust ducts. They pool the heat, which then enters the connected rooms via controlled flaps.
Technical solutions for heat recovery
The process air itself holds the greatest potential for heat recovery. In many applications, the air passes through several treatment stages after the compressor. Filters, aftercoolers and dryers align the properties of the air with the requirements of the respective process. The key components for heat recovery are aftercoolers. The hot process air flows around them. The water-air design variants are suitable for particularly high temperature ranges. They transfer heat energy from the air to the colder water. Operators can directly use this heated water for their processes, or transfer the energy to another medium.
Room heating, hot water treatment and process heat are the most common fields of application in food companies. AERZEN relies on compact pipe bundle heat exchangers for its aftercoolers with heat recovery. The compressed medium flows through the cooler pipes. These, in turn, are surrounded by cooling water flowing in the opposite direction. This design is flow-optimised and causes only a minimal pressure drop in the process air system. This, in turn, contributes to overall efficiency, as blowers or compressors must compensate the pressure loss, additional consuming energy. Powerful process air circuits reliably provide compressed air of the required quality. With integrated heat recovery, they also earn top marks in terms of energy efficiency and sustainability. A prerequisite for this is the precise adjustment of individual components to an overall system. Therefore, AERZEN leaves nothing to chance when it comes to heat exchangers, using a design tool for consulting. It selects the right device for new and old plants of many sizes.
Making waste heat usable
Heat recovery through the transfer of energy from process air to water is an important step. But savings potential only turns financially and ecologically viable when making optimal use of the recovered energy. The heat requirement of the process(s) that can best be supplied with energy must be identified. Several criteria should be observed when selecting these:
- Spatial proximity between heat source and sink
- Reliable supply of the recipient process
- Synchronisation of heat generation and demand
- Sufficient temperature difference between media
Applications for process heat
Nearly every plant can use the recovered heat for sanitary facilities or heating. At temperature levels between 70 and 90°C, water can even replace a heating boiler as a heat source. Furthermore, many process applications for hot water and steam can be found in the food-producing industry, among others:
Here, the energy recovered from the process air plant is usually used to preheat the medium. If the cooling water temperature level falls below the target temperature for the process medium, the solution cannot completely replace the main heat generator. Nevertheless, energy cost savings are immediately achieved by using the recovered heat. For efficient transfers, the temperature difference between the water from the heat exchanger and the target medium should be at least 5, or even better 10, kelvin. It is important that heat recovery can supply the connected processes with heat as continuously as possible. This way, costs for the installation of heat exchangers and lines pay off particularly quickly. This makes the system an attractive option, even for small plants in continuous operation.
Continuous recovery heat flow offers further potential in the new planning of, and replacement investment for, the main heat generator for the target process. The stable heat supply enables you to reduce the capacity reserves for peak heat requirements accordingly. If, on the other hand, the heat from the process air plant is not stably supplied, you, as the operator, require a more efficient steam generator. Gaps in time between the generation of heat and its use requires expensive intermediate storage, associated with great losses. The structural conditions are another criterion for selecting the heat sink. Long transport routes between heat recovery and the process cause higher line costs and energy losses on the transport route.
Integrated solutions are called for
Sustainable process air circuits now have an integrated system for heat recovery. The considerable economic and ecological advantages offset the manageable expenditure in a very short time. This allows operators to keep making long-term economic use of their older plants. Subsidy opportunities, as offered by the Federal Office for Economic Affairs and Export Control (BAFA) with its funding programme for greater energy efficiency, can help realise even quicker amortisation. The scope of eligible measures ranges from the retrofitting of master system controls and heat exchangers to newly designed plants. The use of high-quality heat exchangers and control systems at the heat source is not sufficient to design an effective system for heat recovery. The integration of user processes is at least equally important. Only the efficient interconnection of sources and sinks will have a decisive effect on the efficiency of the entire system.
AERZEN offers consulting, accessories and maintenance from a single source, using the company’s own devices for heat recovery as a basis. They can be retrofitted flexibly and thus enable the energetic optimisation of older plants. This is how AERZEN fulfils its claim to create long-term added value for its clients with its process air systems. The in-house application specialists support the customers in component dimensioning. AERZEN also installs its system monitoring solution at the request of customers. It provides the real-time information necessary for optimal operation and maintenance.