Recuperación de calor

¡Ahorrar energía es fácil!

04/04/2016

Debido a los altos costes de energía y al aumento de la conciencia ambiental, las empresas se ven obligadas a optimizar sus procesos y a utilizar sus recursos de manera más económica y eficiente. Desde un punto de vista económico, la aplicación de recuperación de calor mediante el uso de calor de proceso es cada vez más atractiva. Ahora, AERZEN ofrece conceptos de solución innovadores para reducir los costes de energía de manera sostenida. ¡Ahorros de más del 90% son fácilmente posible!

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La disminución de las fuentes fósiles de energía y el aumento del consumo de energía no sólo requiere más inversión en tecnologías para energías renovables, como la eólica, solar, geotérmica y recursos biológicamente renovables, sino que también implican el crecimiento de futuros mercados estratégicos. Especialmente en el caso de la generación de aire de proceso, el ahorro de energía es muy importante, ya que la mayor parte de los costes del ciclo de vida es el consumo de energía eléctrica. Por razones termodinámicas, en el caso de aplicaciones de aire comprimido, se genera calor (la energía eléctrica de la potencia del convertidor se convierte en calor). Este calor surge como calor residual del motor, compresor y silenciador, pero también se genera cuando aumenta la temperatura del gas de proceso. Sin embargo, en muchos casos, este calor se pierde sin ser utilizado.

En principio, hay dos posibilidades de recuperación de calor cuando operan soplantes de desplazamiento positivo, compresores de émbolos rotativos y de tornillo o turbo soplantes.

Aire de refrigeración para calefacción de espacios

Se puede hacer un buen uso del aire de refrigeración para la etapa, el silenciador y la tubería debajo de la protección acústica, así como la salida del aire del refrigerador de aceite para la calefacción de espacios. Los canales de aire de escape de la unidad agrupan el calor residual (30°C a 60°C). Luego, este aire se transporta como aire de calefacción a los lugares donde se necesita calor. Una salida con temperatura controlada asegura una temperatura ambiental controlada. Dependiendo del período de calentamiento, el exceso de aire se libera al exterior a través de un canal de aire de escape.

La aplicación de los intercambiadores de calor

Otra posibilidad de recuperación de calor es beneficiarse de la energía almacenada del medio comprimido mediante la aplicación de un intercambiador de calor. La ventaja de esto es que el calor se toma del lugar donde se genera. Las pérdidas de energía solo surgen en el camino hacia el usuario final. En el caso de este principio operativo, el medio calentado pasa un intercambiador de calor que calienta el agua que fluye a la temperatura deseada (cuando se trata de las tecnologías de la planta de tratamiento de aguas residuales), o que enfría el gas a 50°C o menos (cuando se trata de neumática) Sin embargo, ambas posibilidades requieren ingeniería con transferencia de calor optimizada. En consecuencia, la cantidad calentada de agua y su temperatura dependen de lo siguiente: velocidad de rendimiento del medio en el intercambiador de calor, longitud del haz de tubería, superficie de la tubería, materiales usados, así como el tamaño del intercambiador de calor. Dependiendo del diseño del intercambiador de calor, el agua calentada se puede usar como agua de proceso. También con este método de recuperación de calor, el agua caliente está alimentando en gran medida al sistema de calefacción. De esta forma, se recuperará más del 85% de la energía térmica.

La generación de aire de proceso es energéticamente eficiente y ahorra costes. Sin embargo, muchos operadores de planta rara vez reconocen estos ahorros potenciales. Gracias a los bajos costes de inversión, los gastos de instalación o integración en el ciclo de proceso de la empresa se amortizan después de pocos meses. Como especialista en aplicaciones, AERZEN ofrece un diseño preciso de intercambiadores de calor con la máxima cantidad de calor transmitido y con la menor pérdida de presión posible. Incluso los sistemas de aire comprimido más antiguos se pueden optimizar y modernizar energéticamente. Otra ventaja: AERZEN ofrece todo de un mismo proveedor.

Heat Recovery with Technologies from AERZEN

Rising energy costs, stricter environmental regulations, and scarcer resources demand innovative solutions from industry. The energy generated for industrial processes should be used as sustainably as possible, conserving resources along the way. AERZEN has long recognised and transposed this requirement. In many applications, the exhaust heat produced by blowers, compressors, and turbo compressors are already recovered and recycled. There are many possibilities for heat recovery. Heat exchangers can convert the heat energy generated by industrial air compression, and use it for a variety of applications: such as water heating, drying, or preheating burner air. Another simple way of heat recovery is redirecting the heated medium. With a cooling flow through the compressor and a sophisticated piping system, the warm air generated in the engine room can be redirected with insulated exhaust ducting, and used for heating other rooms in the facility.

This makes it possible to save heating costs for hot water production, room or hall warming, and warming of industrial and process water. By onward transporting respectively further use of the generated thermal energy by means of exhaust ducting or heat exchangers, also an unnecessarily overheating of engine rooms can be prevented. This way, efficiency losses of the machines due to high ambient temperatures are inhibited. The acquisition of a heat recovery system contributes doubly to sustainable, efficient and conserving applications with high energy savings. The changes that are needed are relatively simple and easy to handle.

Operating Principle of Compressors

AERZEN machines, such as screw compressors and rotary lobe compressors, compress the ambient air sucked in by means of screws. In this thermodynamic process a large part of the electrical energy is converted into thermal energy. On one hand, the heat energy obtained in the compression can be used in the air or gas. On the other hand, the air is heated below the acoustic hood of a machine through radiation from the motor, the compressor stage, the piping, or the silencer. The resulting exhaust heat says nothing about the efficiency of the machine.

In the past, this heat was often lost and was vented out to the open air as wasted heat. The potentials resulting from this large amount of energy are enormous: 85% of the energy that would otherwise be wasted could easily be used for heat recovery. AERZEN, as the market leader in the field of compressor technology, has long been developing energy-efficient solutions for the utilisation of this waste heat for its customers. AERZEN machines are used in a wide variety of applications. Two main applications are pneumatic conveying and wastewater treatment.

Heat Recovery in the Field of Pneumatic Conveying

In pneumatic conveying (e.g. In the industries of food, bulk goods, chemical, or work/industrial materials), the goal is to transport bulk materials such as flour, dusts, sand, or cement by air. AERZEN compressors, blowers, and rotary lobe compressors are often used to generate the needed air flow. During this process exceptionally high air outlet temperatures can be attained. The atmospheric air at a temperature of about 20°C (80°F) is sucked in and can be brought to a temperature of up to 280°C (540°F) during compression, for example, in a screw compressor application. For the conveying of bulk materials, it often must be cooled down again, because the transported materials can otherwise be damaged from the high temperatures. Using a heat exchanger, the compressed air can be extracted from this heat and be used for basic heating, hot water production, or process heat. Depending on the design, the pressure loss due to the installation of a heat exchanger is 1-3% relative to the absolute inlet pressure in the aftercooler. The resulting increased drive power of the motor is disproportionate to the energy saved by the heat exchangers.

Heat Recovery in Wastewater Treatment

AERZEN is a specialist in water and wastewater treatment. The AERZEN machines are often used in wastewater treatment plants for generating compressed air flow, which ensures biological wastewater treatment in aeration tanks. Naturally, this generation of air flow requires a larger portion of the total energy costs of the plant. Therefore, wastewater treatment plants are generally among the largest consumers of electricity in communities and municipalities. This is reason enough for AERZEN to develop energy-efficient and environmentally friendly solutions for customers. In times of increasing environmental regulations and demands in energy efficiency, it is a matter of course for AERZEN to rely on the resource-conserving technology of heat recovery to offer even more sustainable solutions for customers. The use of the right machine technology offers many possibilities and tremendous potential. Even a compressor with a capacity of 22 kW can cover the heat demands of a single-family home. AERZEN can boast about many examples of successful implementations of heat recovery:

Example of WWTP Filderstadt-Bonlanden in Baden-Württemberg

As part of a modernisation and refurbishment project in order to comply with stricter environmental regulations, four Delta Hybrid Rotary Lobe Compressors were equipped with a heat recovery system in the sewage treatment plant, which was constructed as early as the 1960s. This assembly system provides 100% oil and absorption-free compressed medium for aeration tanks efficiently in a very energy conserving way. Free of oil and absorbents not only means benefits in maintenance and service, but also process reliability for the plant. The atmospheric air warmed up by the machines is used by an exhaust system to heat additional technical rooms. However, the substantial savings can be seen by installing a shell-and-tube heat exchanger in the main line of the system. Heat is extracted from the process air stream in the heat exchanger and used for hot water preparation.

Essen-Kupferdreh

In the WWTP Essen-Kupferdreh, AERZEN, as a project partner, achieved highly efficient heat recovery with the plant through a shell-and-tube heat exchanger. The treatment plant uses four positive displacement blowers for the air supply to the aeration tank. The new heat exchanger significantly benefits this application. This built-in heat exchanger supplies the heating and the buffer tank for hot water with heat energy. Altogether, heat recovery in Essen-Kupferdreh saves more than €30,000 ($36,000) annually.

Wertach in Bavaria (Allgäu)

In the wastewater treatment plant Wertach in Bavaria the installation of a new burner could be abandoned. In Wertach, two fixed-speed Delta Blowers are used for basic loads. For higher demands (e.g. for many hikers or winter sports guests) a third blower with variable speed is added .

The 68°C (154°F) air produced by the compression process is cooled to below 30°C (86°F) using an air-to-water plate heat exchanger. This allows the resulting delta of almost 40°C (104°F) to be used to supply the boiler water to the boiler itself. The pressure loss of the process air in the heat exchanger is considerably low. If no heating is required (say, during the summer), switching is easy. Through a mechanical valve in the piping the air can be passed directly into the ventilation tank instead of going through the heat exchanger -- this way, a needs-based control and heat recovery is always possible. With heat recovery, the plant reached a heating oil savings of about 1,850 liters (490 gallons) per year.

When is Heat Recovery Worthwhile?

Before deciding to purchase anything for heat recovery, several factors should be considered.

For example, the structural conditions must be taken into account: the spatial proximity of the waste heat source and the heat sink is important. If these are too far apart, transport losses and increased costs for piping must be taken into account. If the cost of storing and transporting heat is high, higher investment costs are also to be expected.

In order to ensure that the installation of a heat recovery system pays off, there should also be a T of at least 5-10 k between the waste heat source and the heat sink.

Simply, the use of heat recovery is particularly valuable for larger units and continuous production processes. But even with low levels of heat waste and high capacity utilisation at the same time, a heat recovery system would be worthwhile to have. In principle, a heat recovery system is the more worthwhile as more continuously the assemblies are in operation.

Résumé:
The high-energy demand, which is used in production of compressed air, can be recovered and used in many ways. With AERZEN technologies and know-how, new projects in wastewater treatment or Pneumatic Conveying can be designed to use heat energy for rooms, hall heating, or water warming (processing or service water) or for production processes. The examples of possible uses are diverse:

Feed of central heating systems
Warm air heating
Sludge drying
Hot medium for process tasks (e.g. drying processes in production)
Production of hot water for shower and washrooms
Service water heating for canteens
Construction of hot air locks
Preheating of burner air
Pool heating

Existing plants can also be modernised and made more efficient by basic means. AERZEN offers customers a wide range of services in this area (e.g. a 24-hour telephone information service, a machine diagnosis or the AERaudit), where service employees develop a plan for the modernisation of a plant.
With the aid of the AERZEN room ventilation calculator, technicians and wastewater treatment plant owners can also find the appropriate heat exchanger for their plant themselves.