Energy conservation issues are becoming increasingly acute as capacity is building up on modern consumers. In both the domestic sphere and in industry, the used technical means, aggregates, and communication networks require ever-increasing volumes of energy resources. This forces us to look for new, alternative sources of heat, electricity and other types of energy. Despite the active development of natural natural energy carriers, this segment still does not allow reckoning on the complete crowding out of traditional generator stations. At the same time, secondary energy resources (WER) are of considerable interest, which are largely free, but require less investment in the creation of a service infrastructure. However, the features of the secondary energy product do not end there.
Definition of VER
There are two fundamentally different ways of generating energy - natural and industrial (artificial). In the first case, the energy of natural phenomena and processes is used - for example, the flow of water, solar radiation, wind, etc. The complexity of the use of such resources is caused by technical problems of an organizational nature - in particular, the instability of energy storage. Industrial energy generation in this sense is more controllable, but it requires raw materials to provide reactions during which heat, electricity, gas, etc. are generated. The combination of primary and secondary energy resources takes place within the framework of the operating cycle of generating stations. The fact is that the main resources are not fully used, and their residues are subsequently disposed of or recycled. On the same basis, secondary energy production stations operate.
When considering the principles of using VER, it will not be superfluous to turn to the concept of energy potential. This is the amount of energy that theoretically can be generated during the processing of waste, by -products of production and intermediate raw materials that are not consumed in the primary cycle. Moreover, the expression of the potential in the form of energy can be different. Reserves of certain wastes are represented as physical or chemically bound heat, overpressure, kinetic energy or fluid pressure.
So, the definition of secondary resources for the operation of power plants is as follows: this is the energy potential that can be generated as a result of the technological process of processing underused waste or products of the main production. At the same time, the waste itself and the methods for its further processing can be different.
VER characteristics
It is worth noting that for a long time this concept of energy generation was not considered by large consumers due to the lack of accurate methods for calculating efficiency and energy potentials. Today, the recycling of resources is based on a comprehensive analysis of a wide range of indicators, which makes it possible to extract the maximum benefit from the same production waste. The most common design characteristics of this type of resource include the following:
- The output energy coefficient is the ratio of the generation potential to the thermal volume that entered the generator with primary resources.
- Energy consumption coefficient - the ratio of the volume of consumed heat from the secondary generation to the energy received in the generator set. This indicator reflects the efficiency of using a specific energy scheme of the enterprise. Moreover, there are different ways of assessing optimal consumption volumes - with a focus on economically feasible values, actual and planned consumption indicators.
- Fuel economy opportunities are the amount of primary resources that are not consumed through the use of industrial waste. Moreover, savings can be calculated according to the reverse scheme, when primary and secondary resources replace each other depending on the current conditions of heat or electricity production.
- Utilization rate - the ratio of the volume of generated heat to the energy potential of the resource received in the processing boiler.
- Energy generation coefficient - the amount of energy that is directly generated when using secondary raw materials in a recycling unit. It should be noted that the generation coefficient differs from the output energy by the amount of heat loss in the working installation.
- The operational coefficient is a value that determines the difference between the planned energy output and the actually generated production volume through the ratio.
Choosing the optimal VER model
In each case, when developing a project for energy supply through secondary resources, the economic task is brought to the forefront, the essence of which is the use of the most effective raw materials. To do this, a preliminary certification of all available sources of secondary resources is carried out with an indication of their reserves, pollution, temperature and mode of receipt. It also defines the requirements for ensuring the technological processes of utilization of water and energy resources. Depending on the operating conditions of the enterprise and the method of processing raw materials, these can be heating, ventilation, gas and water supply systems.
At the final stage of project creation, the following procedures are also performed:
- The most economically feasible method of disposal is selected according to one selected or several sources of secondary raw materials.
- The economic effect of each resource processing activity is determined.
- A scheme for the operation of the disposal plant in accordance with the needs of the enterprise is being developed. Also, the main technological process can be supplemented by auxiliary operations of the type of cogeneration plants - for example, if conversion of several types of fuel is required.
Sources of secondary resources
In a general sense, VER sources are understood as a combination of technological processes and processed raw materials in the framework of the operation of primary energy generators. Also, different production areas can act as sources of material for the subsequent generation and conversion of heat or electricity. What is related to secondary energy resources? Specific types of materials are determined by the scope of primary production of raw materials. For example, metallurgical enterprises produce scrap, waste non-ferrous and ferrous metals, rubber mixtures and unused alloying additives.
If we are talking about heat supplying consumers, then furniture and paper mills, as well as construction woodworking enterprises that provide fuel combustible materials will come to the fore. The following examples of secondary energy resources of this type can be given:
- Peat briquettes.
- Wood chips and bark.
- Ash from high temperature drying boilers.
- Lignin.
- Waste paper.
- Solid wood waste.
- Unclaimed paperboard products.
As the technological processes of production become more complicated, the structure of waste with emissions also changes. Along with traditional raw materials, high-quality and complex multicomponent wastes are increasingly used in secondary processing cycles. These include the following materials:
- Polymer thermoplastic elements.
- Agglomerates of synthetic alloys.
- Rubber products and regenerates.
- Halite waste.
- Blast furnace slag.
- Phosphogypsum.
Along with this, the level of environmental threats is increasing. If one of the most important advantages of natural natural energy sources is the ecological purity of the generation processes, then high-efficiency WER is to a large extent provided by contaminated and chemically aggressive substances that are not amenable to primary processing. These include petroleum products, sludge and sludge, worn tires, mercury-containing wastes, etc.
Classification by directions of use
One of the key classifications of secondary resources, which determines the scope of application of energy-valuable raw materials. As a rule, the following areas of use of VER are distinguished:
- Fuel combustion in units using raw materials ready for heat treatment. A simple heat production scheme is implemented without intermediate stages of processing and conversion.
- Thermal use. Generation in thermal recovery units. In contrast to the previous method of using resources, the cogeneration principle of energy generation can be implemented, but also without conversion operations. For example, on different lines of the generator station, the use of secondary energy resources allows you to receive heat, hot water or steam.
- Thermal and combined use. Along with heat generation, conversion to electricity is also carried out. For example, turbines generate electricity in heating or condensation forms of energy.
- Electric power. Electricity is generated using a utilizing gas turbine unit.
Media Type Classification
Under the carrier is understood the form of the energy resource, as well as its agrotechnical state, under which the utilizing plant will be selected. On this basis, the following recyclable resources are distinguished:
- Liquid, solid and gaseous waste.
- Pairs - worked out and passing.
- Flue gas.
- Intermediate and finished manufacturing products.
- Technical cooling water.
- High pressure gases.
Classification by main types of VER
The most common are combustible and thermal secondary resources for processing at utilizing energy substations. For example, combustible WERs, as a rule, represent industrial waste used in the form of finished fuel for other production tasks. In this case, the following classification of secondary energy resources is applicable:
- Metallurgical blast furnace gases.
- Wood waste in the form of wood chips, sawdust and shavings.
- Liquid or solid waste used in the refining and chemical industries.
Thermal VER provide physical heat without conversion. In this capacity, process exhaust gases, industrial by-products, slag and ash, direct heat from operating units and apparatuses, steam and hot water can be used. It is important to emphasize that heat resources can be used both directly as a heat source, and in the form of raw materials, the processing of which will contribute to the generation of electricity.
Less commonly used are resources whose potential energy is generated from sources of excess pressure. These are the types of secondary energy resources that can be emitted, which can be steam and gas mixtures leaving the work units in the atmosphere. Such resources are divided according to the level of energy concentration and temperature indicators. Now we can consider each of the mentioned types of VER individually.
Combustible secondary resources
In the share of global use of VER, combustible fuel occupies about 70-80%. The main type of such waste is wood and its products. The target equipment for utilization of the resource is usually boiler and furnace units that provide technological processes of combustion with a heat sink. Russia also has specialized installations for the processing of combustible types of secondary resources - for example, lignin is processed at hydrolysis plants, but due to the difficulties in servicing products, such technological approaches are not common.
Car tires are also classified as secondary combustible waste, and their utilization with the release of energy is carried out in three ways:
- With the connection of a cascade of crushers for preliminary grinding.
- Using continuous compression systems in a closed volume in special extruders.
- With cryogenic grinding technology, which uses liquid nitrogen.
Combined methods of burning combustible products are also popular. After sorting the raw materials according to certain criteria (fraction, degree of contamination, chemical and structural composition), secondary processing of resources of one type is carried out. So, together with wood waste, coal and rubber crumb can be burned if it is suitable for the given technological characteristics. At some recycling stations, the preparation of combustible waste for further production is also carried out. In particular, building materials like hoses, mastics, fillers for various mixtures and paints are made of activated carbon, radio engineering elements and composite materials after energy processing.
Thermal secondary energy resources
The energy potential of VER of this type also allows them to be widely used in a wide variety of industries and industries. The most valuable heat resources in terms of productivity are exhaust gases produced as a result of chemical reactions, pyrolysis and combustion of the main fuel products. Condensate heat is also used, although due to the technological complexity of energy extraction processes, this source is used only in multifunctional large enterprises with cogeneration plants. Theoretically, heat can be generated from ventilation emissions and other engineering networks with hot streams of air and water, but its share in the total volume of secondary energy processing is only 2-3%.
There are also restrictions on the use of heat sources of secondary energy resources, which are imposed on the supply air heating systems. In particular, technological use of the following air media is not allowed:
- Streams removed from rooms containing flammable or explosive substances. Even if the sampling point is indirectly associated with combustible gases or vapors through ventilation ducts, this air cannot be used in heat recovery units.
- Streams that can become carriers of harmful substances. This usually happens when the circulating air collects condensing or precipitating particles from the processing of hazardous materials from heat exchangers.
- Streams that may contain pathogenic viruses, bacteria, and fungi. Biological contamination of the air is also caused by the specifics of a particular production or the operating conditions of the engineering system.
A characteristic feature of the use of secondary resources for the purpose of heat generation is the seasonal mode of operation of utilization plants. This is due to the fact that a significant part of the processing boiler houses is activated during periods of heating with a direct intake of thermal energy. This is especially true for utilities, but in industrial production, thermal support for technological operations is carried out at the pace of the local schedule.
Secondary resources under pressure
Mostly this is industrial waste resulting from primary processing processes. It can be gases, liquids, and even bulk solids. Their main feature is being under excessive pressure when exiting a work unit or engineering system. It is the requirements for pressure regulation that make it difficult to use this type of secondary resources, as well as their derivatives. At a minimum, the processing cycle should include a pressure reduction operation before discharge. For this, special regulators with gearboxes are used, which automatically normalize the state of the bodies to optimal performance.
Equipment for VER service
Utilization plants are used to extract energy from secondary resources, which can provide different processes of processing and production. There are both specialized and universal units. , , . , , , .
, :
, , . , . , , , , . .
, . , . , 250 °, . . -. .
The effectiveness of using such heating technologies is low and amounts to only 10-12%, but taking into account the absence of costs for raw materials, this approach justifies itself. Another thing is that the use of secondary energy resources in itself requires the initial organization of conditions for heat production and the subsequent distribution of combustion products through heat-exchange networks. Additional equipment for production lines may be required to remove unwanted suspensions and basic cleaning systems.
Heated open areas using VER
The creation of working areas with technological equipment outside the premises, according to various estimates, can save from 10 to 20% of the estimated costs of organizing production processes. Of course, there is no question of a complete exit outside the workshops, but minimizing the volume of building structures when creating such sites significantly reduces the cost of projects. But along with this, the operation of the equipment will be difficult due to the presence of snow and ice on the sites. Accordingly, there is a need to organize a heat supply system in an open area. The choice of a specific installation and the type of secondary energy resource will also depend on the direction of the enterprise and its technological waste. As a rule, water circulating in the annulus with a return to the heating source is used as a heat carrier. To maintain optimum fluid parameters, antifreeze is additionally used, and flow control is carried out by automation with buffer expansion tanks.
Heat transfer will depend on the volume of the resource, the design of the pipeline and external microclimatic conditions. In order to maintain safety during the operation of the system in winter, it is recommended to arrange special coatings on a concrete basis. Also, in the interest of increasing thermal conductivity, technologists advise covering the structure with solutions based on heavy concrete, basalt chips and granite inclusions. If we are talking about cold regions with severe frosts, it is better to choose a secondary energy resource based on water with the addition of snowmaking installations in the working infrastructure . The estimated amount of generated heat for melting snow masses and ice will be approximately 630 kJ / kg. If the design of the system does not allow the accumulation of snow on the work site, then the energy consumption for its melting at the time of precipitation will increase to 1250 kJ / kg.
Benefits of Using VER
The use of alternative energy sources, as a rule, is determined by economic, technical and environmental factors. In this case, all these factors work, but the economic one is dominant. With a well-implemented project for the implementation of the utilizer at the enterprise, one can count on reducing the cost of heat supply, for example, up to 25-30%. A specific indicator of savings is determined by the conditions of production and the use of secondary energy resources, but the benefit will be in any case. Especially if local and own processing materials are used at the target enterprise.
Another advantage is associated with the high energy potential of the waste. Gases, process fluids and solid-state industrial raw materials are initially selected according to the principles of maximum extraction of large volumes of heat. Moreover, in contrast to the operation of the main traditional energy carriers, the secondary resources at the time of use are already in the aggregate and temperature state optimal for processing.
Disadvantages of using VER
The widespread dissemination of this concept of energy supply is hindered by several factors, the main of which is the complexity of the technological structure of such systems. Even if you do not take into account the cost of equipment in the form of utilizers, with the technical organization of the process, the reconstruction of the operation site will inevitably be required, since the system will work in conjunction with different engineering units.
Another drawback from the use of secondary resources can be represented as low rates of energy return. Again, given the free supply of this raw material, economic feasibility will be positive, however, a modest percentage of heat transfer, in particular, will not allow counting on the construction of generator stations for complex servicing of production facilities and other consumer goods. As a rule, this is only an auxiliary source of energy.
Conclusion
Resources for processing for the purpose of secondary energy extraction have fundamental differences, both from traditional and natural sources of energy supply. Partly they are caused by the very origin of this raw material, but to a greater extent - by the specifics of the technology of their application. At the same time, the consumption of primary and secondary resources can occur within one production process. For example, if fittings are manufactured at the plant, and the products of combustion from blast furnaces are sent to utilizers with heat exchangers that serve other technological operations. A full production cycle is being implemented, which is characterized by higher efficiency, rational use of resources and environmental friendliness, since waste is being processed.