Utilization and heat recovery. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Before talking about utilization and heat recovery, it is necessary to define these similar concepts. Utilization (use) involves the use of heat for various purposes. Recovery (return) refers to the return of heat to a dwelling, production process, etc.

No matter how much we improve heat generators, no matter how we insulate and seal our houses, all 100% of the heat produced will sooner or later leave the dwelling. The breathing process, which requires ventilation, is to blame for everything. During ventilation, together with the used air, heat also leaves our housing.

The idea of ​​somehow utilizing heat emissions is not new. The simplest device that makes it possible to use the decrease in the density of gases when they are heated is the well-known chimney. This, as heat power specialists say, is a fixed straightener that provides draft in the furnace, which, in turn, allows you to achieve a higher combustion temperature of the fuel. An example of room ventilation is a fireplace. Today it is mistakenly considered a heat generator. But the heat generator from the fireplace, frankly, is useless: in terms of efficiency, this device occupies the last place among all known heat generators.

The idea of ​​heat recovery in metallurgy is especially relevant. More than half of the energy consumed by industry, and more than a third of the coal mined, is directed precisely to the needs of metallurgy. Heat exchangers allow using the heat of metallurgical processes to heat the blast blast. Such devices can also be used for heat recovery in residential premises [1].

The scheme of forced ventilation with heat exchange between incoming and outgoing air is shown in Fig.1.

The electric fan drives the used air through the heat exchanger. At the same time, fresh air enters the room heated. To increase the degree of this heating, it is necessary to increase the pressure of the exhaust air discharged to the outside. Often used for heat recovery gases (air, steam, smoke) contain various contaminants that clog heat exchangers. To prevent this, again, it is necessary to increase the pressure of the gases used for heating in the heat exchanger. This can be done with the help of a throttle - a hole of small diameter that prevents the free movement of gases. By increasing the air pressure to 30-40 atm., you can heat it over 700°C. The property of gases to increase their temperature when compressed is used in diesel engines, air conditioners, when liquefying gases, etc.

But it is energetically impractical to use a choke to concentrate heat. To increase the efficiency of heat recovery and heat recovery devices, instead of a throttle, it is necessary to use expanders, preferably based on a tangential turbine (vortex turbine) Fig. 2, where 1 is a spiral gas supply, 2 is a directing nozzle apparatus, 3 is a rotor, 4 is an outlet diffuser.

In essence, expanders are nothing more than pneumatic motors in which the gas, expanding, does work and is greatly cooled. Today, turboexpanders are used where they are almost indispensable: to liquefy hydrogen gas, which, when passing through the throttle, is not cooled, but, on the contrary, is heated.

Today, expanders are loaded with specially cooled water brakes. The heat of the resulting boiling water is utilized by means of a cooling tower - a vertical pipe of a very large diameter (Fig. 3).

In a cooling tower, heat is used to cool water by hyperconvection of atmospheric air. These devices were invented hundreds of years ago and today they are already morally obsolete, they are being replaced by more efficient and compact heat pumps that allow using low-potential heat at 100%. It should also be remembered that cooling towers are one of the biggest sources of thermal pollution of the atmosphere.

If the expanders are loaded not with brakes, but with compressors, electric generators or used as engines, then some of the energy expended in compressing the gas can be returned, while the efficiency of heat exchange units increases.

To save electricity for heat heating, it is possible to use various types of heat pumps, but the most interesting are units in which heat recovery is combined with motion or electricity recovery.

Figure 4 shows a heat exchanger that performs the functions of a ventilation unit and a heat generator.

As a working fluid, air is used from a room ventilated and heated by this heat engine. The load (compressor) is distributed by means of a differential between the electric motor and the expander. Drivers are familiar with the operation of a differential in a vehicle's drive axle.

The design of the turbocharging unit, consisting of a compressor and an expander, is also known to many. The use of turbocharging in air conditioners increased their efficiency by 2 times. If turbocharging is used in the recuperator (Fig. 5), then the need for a differential will disappear.

But the most tempting is the idea of ​​using a tangential turbine-expander to drive an electric generator (Fig. 6).

The operating speed of the turbo expander is huge (tens and even hundreds of thousands of revolutions per minute), which allows the use of generators with high power density and efficiency. With a sufficiently powerful heat exchanger, supercooled air can be obtained at the outlet of the expander, which will make it possible to use electric generators based on superconductors. Today, superconductors are already being made by schoolchildren [2]. To do this, a mixture of yttrium, barium and copper oxides is sintered for 8 hours in a ratio of 1:2:3. Such a material exhibits superconductivity already at liquid nitrogen temperature (77°K).

Today, more than ever, it is important to think about saving heat and electricity. Heat pumps and recuperators based on them will greatly assist in the implementation of almost 100% savings.

The use of these devices will dramatically reduce the loss of electricity and heat in our homes. But most importantly, recuperators will significantly reduce harmful emissions, which already today lead to unpredictable and catastrophic changes in nature.

References:

1. Heat recovery//Electric. - 2001. - N9. - C.3.
2. Tuchinsky L. To whom luck smiles. K.: 1990, 125 p.

Author: Y. Bearded

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