Utilizers, economizers

What are recyclers

In heat devices and machines of various types, such as furnaces, boilers, turbines, internal combustion engines operating on combustible fuel, a significant part of the generated thermal energy is removed with waste (furnace, exhaust) gases and irretrievably lost. It is known that the efficiency of even the most economical heat engines, such as steam and gas turbines, barely reaches 40 - 45%. Even greater losses of thermal energy occur in industrial technological processes in which the receipt of thermal energy is not an end in itself, for example, in melting or heating furnaces and chambers, chemical and food reactors, heaters, etc.
Thermal energy for industrial, economic or domestic purposes is, in the overwhelming majority of cases, consumed combustible fuel (oil products, coal, wood, combustible gases, etc.) or electricity of significant material value. Therefore, all the possibilities for saving them are of great commercial interest. One of the effective ways to save material resources and obtain additional volumes of thermal energy for industrial, economic and domestic purposes is its utilization from waste (exhaust) gases. Technically, this problem is solved using utilizers, or economizers.
The waste heat exchanger ( economizer ) is a recuperative-type heat exchanger-heat exchanger, located in the exhaust gas discharge channel, in which heat is taken from the hot exhaust gases and the cold channeled coolant is heated. Cold water usually acts as a heated heat carrier in utilization systems. The result of such heat exchange is the utilization of some (often very significant) part of the thermal energy of the exhaust gases, and the production of hot water vapor or hot water, which are consumed in the interests of water or steam heating, hot water supply, and technological heating.
For utilizers (economizers), there is a concept of the utilization depth, which is expressed in the degree of cooling of the exhaust gases. For multistage ("multi-storey") economizers, a fairly large utilization depth is possible, with exhaust gas cooling from an average of 300 ° C to 50 ° C.

Types of utilizers, design

As one of the options for the implementation of heat exchange equipment, the most common are heat exchangers of two types:

• according to the "shell-and-tube type", with a water supply heat exchange pipe (usually finned) in the form of a coil, which is located in the discharge gas channel (furnace, exhaust pipe);
• according to the "lamellar type", in the form of a lamellar heat exchange structure, through one channel network of which hot exhaust gases pass, through another channel network - heated water.

The heat exchanger of the heat exchanger (coil or plate type) is placed in a housing, which, in turn, is mounted inside or in a section of the exhaust gas discharge channel. Corresponding nozzles or flanges are attached to the body for connection to the plumbing system.

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Fig. 1 Diagram of a coil-type heat exchanger

Fig. 2 Scheme of a plate-type heat exchanger

Depending on the number of heat exchange elements, economizers can be: single-body and multi-body, one-, two- or more power ("storey"), one-pipe (single-coil) or with several coils. In waste systems with a very high temperature of exhaust gases (400 - 600 degrees C and more), heat exchangers made of heat-resistant materials are used. For systems with a deep utilization rate, when part of the moisture from strongly cooled exhaust gases (up to 50 degrees C), with gases CO _x , NO _x dissolved in it, precipitates in the form of "acid" dew, heat exchangers made of corrosion-resistant stainless steels are used.

But the economizer heat exchanger itself is the most important, but still only part of the complete utilization system. The overall design must also include a set of pipes and pipeline fittings, pumping equipment, protection against hydraulic and thermal overloads, control and measuring instruments, control means (equipment), systems for the selection of heat energy or hot water for consumer or technological purposes. Complex technical systems for utilization of waste gas heat energy are called utilization boilers.

Fig. 3 Scheme of a steam waste heat boiler

Fig. 4 Diagram of a waste-heat boiler

Principle of operation

The principle of operation of a heat exchanger (economizer) is classic for heat exchange equipment. Hot exhaust gases, acting as a heating coolant, under the influence of pressure created by a heat generator or furnace draft, pass through the economizer through their heat exchange channels. In the opposite direction (counterflow) through its channels (or through a finned tubular coil) cold water is pumped, which becomes hot during heating, or turns into saturated water vapor. Subsequently, the cooled exhaust gases continue to flow into the waste system, hot water or steam is supplied to consumers.

Scope of application

The scope of application of waste heat exchangers can be divided into areas: industrial and economic.

In the industrial area, the source of utilization of thermal energy can be a wide variety of technological processes, in which either the generation of excess heat or its incomplete consumption occurs. The consumption of recovered heat (steam or hot water) can occur in the interests of maintaining certain technological processes, but most often - for heating production premises (workshops) or providing hot water supply to the enterprise.

In the economic field, the source of utilization of thermal energy in most cases is heat generators of heating systems and (or) hot water supply, such as central boiler houses or separate boilers (stoves). The consumption of the obtained hot water occurs mainly in the interests of centralized or local water heating and (or) hot water supply.

Fig. 5 Wiring diagram for household class economizer

Technical characteristics, parameters for the selection of heat exchangers

As a rule, waste gas discharge systems in industrial plants have a lot of individual differences. Whereas the heat engineering conditions created by boilers for household or domestic purposes are much more monotonous (typical). Therefore, utilization systems for industrial and large utilities usually require individual design, for small-sized typical boiler houses or household heating boilers (stoves) - they can be selected from serial (typical) models.

The main technical characteristics of utilizers (economizers) include:

• heat exchange area, m2;
• thermal power, W;
• water or steam capacity, m3 / h;
• working pressure in the water circuit, Bar
• maximum and operating gas temperature at the inlet;
• outlet gas temperature;
• aerodynamic resistance, Pa;
• hydraulic resistance of the water circuit, Pa;
• material of manufacture (heat-resistant, corrosion-resistant).

For a high-quality selection of a heat exchanger for your exhaust gas removal system, you should know (determine) its such parameters:

A) Properties of exhaust gases:

• physical density;
• dew point for gas components;
• chemical composition;
• contamination and tendency to deposits.

B) Conditions in the discharge system (chimney):

• gas temperature at the inlet and outlet;
• quantitative consumption of exhaust gases (volumetric or mass);
• heat flow;
• calculated gas pressure;
• permissible gas pressure loss in the heat exchanger.

C) Required parameters for the water circuit:

• inlet water temperature;
• required leaving water temperature;
• required capacity for hot water;
• operating pressure;
• permissible pressure loss (hydraulic resistance);
• estimated service life.

Advantages of utilizers produced by OPEKS Energosystem

OPEKS Energosystems has many years of experience in the design and manufacture of heat exchange equipment for a variety of temperature conditions and aggressive environments, of various scales and purposes. We have undeniable authority on the market as a supplier of heat exchange equipment of consistently high quality.

Utilizers and economizers OPEKS:

• are carried out only according to waste heat engineering schemes, which have proven their effectiveness in practice;
• are designed by experienced heating engineers who know and take into account the physical and chemical processes that take place in different waste gas discharge systems;
• very accurately calculated and designed for the conditions of a specific exhaust gas discharge system, according to the customer's requirements;
• are made of high-quality, heat-resistant and corrosion-resistant materials, with strong and sealed joints, which guarantee the absence of burnout of the heat exchanger under any operating conditions, throughout the entire standard service life.

When designing and manufacturing waste heat exchangers, the possibility of their operation at high temperatures of exhaust flue gases, in some cases reaching values of more than 280 ° C, is taken into account; also, the cooling of flue gases can be so deep (up to 50 ° C) that the temperature of the cooled gas at the outlet will be below the dew point of the water vapor in the flue gas. This can be the reason for the increased acidity of the condensate as a result of the reaction of the water condensate H ₂ O with the gases NO _x and SO _x . For such cases, condensing heat exchangers or economizers are made of corrosion-resistant stainless steels.

The efficiency of utilizing heat exchangers is so high that the payback period for the entire complex of works on calculation, manufacturing, installation and commissioning is within 6-10 months, depending on the volume and temperature of flue gases. The generation of additional heat and the associated fuel savings provide a significant increase in the economy and efficiency of production in general.

The principle of operation of a heat recovery unit manufactured by OPEKS Energosystem