Utilization of thermal energy. Development, design and operation of low-grade heat recovery systems
Page 1
Utilization of low-temperature thermal energy in condensers of steam plants and heat exchangers gas installations can in principle be considered as one of the possible areas of application of thermoelectricity.
Utilization of the thermal energy of exhaust gases from boiler houses, diesel and gas turbine plants, regeneration of the thermal energy of the latter, production of heated water in contact water heaters, evaporative cooling and hygroscopic desalination of water, heat and humidity air treatment and wet gas purification - this is not a complete area of application of contact devices. This is explained, firstly, by the simplicity of their design and insignificant metal consumption compared to recuperative surface heat exchangers, and the possibility of manufacturing from non-metallic materials; secondly, by increasing the efficiency of installations due to more complete use of thermal energy, the possibility of improving the parameters of the thermodynamic cycle, regulating the flow of the working fluid, internal cooling or heating of the installation; thirdly, - the possibility of creating new installations and their technical systems, providing reduction in fuel, water, materials consumption, increasing power and productivity, improving working conditions and reducing pollution environment. The possibilities of using heat and mass transfer processes in contact devices of energy and heat-using installations have not yet been fully disclosed. This is facilitated by the existing purely empirical approach to calculation, which does not allow identifying the internal connection physical phenomena V complex processes heat and mass transfer, reflect this relationship in calculated dependencies and use it in practical activities.
The installation is designed to utilize the thermal energy of waste (spent) steam from autoclaves in the existing production of sand-lime bricks. Autoclave treatment of raw bricks with saturated water steam is the final stage in the production of sand-lime bricks, consuming a significant amount of energy resources. In this regard, the issue of ensuring more complete use of the thermal energy of exhaust steam after autoclaves and recovery of the resulting condensate is an urgent task.
The most common schemes for recycling the thermal energy of exhaust gases from piston engines include equipment for producing steam with a pressure of up to 15 kg/cm, or hot water with temperatures up to 100 C, or direct use of waste gas heat in drying processes.
This made it possible to approximately double the utilization of thermal energy and bring it to 22 million Gcal in 1985. Reconstruction of heat exchange units at 12 existing installations primary processing oil and the modernization of technological furnaces made it possible to save almost 1 million tons of standard fuel in the eleventh five-year plan. Due to the use of additional quantities of refinery gas as fuel, which is currently burned in flares, as well as the introduction of 450 advanced air heating devices, 0.5 million tons of standard fuel were saved. During the years of the Eleventh Five-Year Plan, the industry saved about 900 million kWh of electricity and 1 8 million tons of standard fuel.
These blocks (Fig. 3.49) are designed to utilize low-grade thermal energy from ventilation emissions due to convection in heat exchanger blocks using aqueous solutions of glycol and ethylene glycol of various concentrations as a coolant.
Along with the advantages, the method of burning oil sludge has a number of disadvantages, the main of which are the difficulty of utilizing thermal energy, the bulkiness of the equipment, and air pollution, which does not always allow us to conclude that the use of this method is inappropriate.
The described installation scheme for using waste steam heat and condensate recovery makes it possible to fully and highly efficiently utilize the thermal energy of waste steam and return the resulting condensate for reuse both in the technological process and in a closed water supply system to obtain saturated steam at the boiler plant.
Maintaining technological process on particularly complex installations various systems for separate and simultaneous combustion of liquid, solid and gaseous waste chemical production, technologically related to the utilization of thermal energy and operating on solid, liquid or gaseous fuel.
Conducting the technological process of combustion of waste gases, natural gas, industrial wastewater, still remains and solid waste in combustion furnaces of various designs with the simultaneous management of lower-skilled operators, as well as maintenance of complex installations of various systems for the combustion of liquid, gaseous or solid waste from chemical industries that are not technologically related to the utilization of thermal energy or chemical raw materials.
There is an erroneous point of view that the use of low-grade heat from this source is of little practicality. At the same time, the utilization of thermal energy of steam distillate fractions would significantly reduce the consumption of circulating (or direct-flow) water, as well as reduce the thermal power of furnaces. If only 50% of the heat removed in condensers and refrigerators is used to preheat raw materials, then oil with an initial temperature of 10 C can be heated to 82 C.
Heating of cold Tyumen oil, selected at the headworks in one of the regions of Tatarstan, and its subsequent transportation within 10 - 180 minutes. It follows that desalting of Tyumen oil under soft operating parameters can be carried out on its way to the refinery and in cases where the effect of self-heating of oil during transportation is eliminated, but there are reserves of thermal energy to be utilized.
This not only pollutes air environment, but the resulting thermal energy. A number of experts believe that it can only be justified if thermal energy recovery and waste gas purification are combined. This process occurs at waste incineration stations (factories) that have steam or hot water boilers with special fireboxes. The temperature in the firebox must be at least 1000 C so that all foul-smelling impurities burn out. However, before being released into the atmosphere, gases must be purified, for example using electrical filters.
From a practical point of view, it should be noted that if the final stage of software processing and disposal technology is known, then they should be classified based primarily on this technology. The final stage of neutralization of most non-recyclable urban software (excluding particularly toxic ones, as well as inert construction garbage etc.) is currently burning. This is confirmed by the experience of centralized software neutralization in countries such as Denmark, Finland, Germany, Sweden, etc. With this technology, it is important to group all waste so that it organically flows into one or another technological chain leading to ultimate goal- - thermal neutralization of waste with utilization of thermal energy and other healthy products. Based on this, it is necessary to distinguish between combustible and non-combustible waste, within which, in turn, there are also differences in properties, phase state, processing methods, etc. Separately, it is necessary to highlight waste that can mutually neutralize each other or serve, for example, as reagents for processing emerging Wastewater. Waste containing especially useful components, such as non-ferrous metals, must be separated and processed separately so that the final product does not mix with less valuable slurries. It is necessary to determine the heat balance between combustible and non-combustible waste, the internal heat demand of the centralized disposal station, the need for additional fuel, or the volume and ways of utilizing excess heat. This should determine the nature of the questionnaires or forms for one-time waste accounting.
Ph.D. Baron V.G., Director of Teploobmen LLC, Sevastopol
Currently, energy saving issues are receiving increasing attention, various options for reducing energy costs are being increasingly sought, are being considered and implemented, including with the involvement of significant funds, a variety of schemes designed to reduce energy consumption. At the same time, it is still the exception rather than the rule that heat is collected from various types of cooling liquids for the purpose of its subsequent use. In most cases, this is heat (unfortunately, often low-grade) in huge quantities dissipated into the environment through cooling towers, open-loop water cooling systems, and simply by convective heat exchange with the surrounding air. As a result, thermal pollution of the environment occurs, funds are spent unproductively on the creation of such, let us note - not cheap, systems, and, most importantly, energy is wasted aimlessly, which is generated in parallel, often to cover the needs of the same consumer, by generating capacities. There are many reasons for such inattention to the energy source in the form of waste heat from various cooling systems. Moreover, until recently the main ones were objective reasons- extremely large mass-dimensional characteristics of the primary means of heat removal, i.e. heat exchangers, and their, largely due to this, high cost and complexity of layout at the facility. In addition, a limiting factor was the high cost of heat pumps designed to transform waste low-grade heat, increasing its temperature level, into a product that can be further used. It should be noted with regret that today, despite the fact that among these reasons there are practically no objective ones, the process of energy saving through reuse the heat in question remains at the freezing point. Now most of the reasons are not enough active use of these secondary resources already lies on the subjective plane. This is both inertia of thinking and lack of knowledge about modern technical devices capable of effectively solving such problems. In this case, it is meant that it is already possible to transfer low-grade thermal energy to a higher temperature level using heat pumps, and also, as the first condition for this, there are highly efficient heat exchangers for removing low-grade heat. Highly efficient heat exchangers are the first and indispensable condition because in order to utilize waste heat it is necessary, first of all, to carry out its effective transfer from the coolant to some kind of coolant, from which this heat can then be transferred either directly to the consumer, if there are processes that require heat low temperature level, or transferred to the heat pump cycle to improve the energy quality of this heat. In previous years, the lack of effective heat transfer devices, especially for viscous liquids, along with the lack of effective heat pumps, objectively hampered energy saving through waste heat recovery. Today, such devices exist and consider one of the modern heat transfer devices, created specifically for the purpose of selecting low-potential heat from thermally complex environments - motor oils, this article is devoted to.
These devices are created by modifying effective heat exchangers of the TTAI type to meet specific conditions of heat exchange with highly viscous media. TTAI devices created by employees of Teploobmen LLC using the experience accumulated during many years of work on creating heat exchangers for the needs of the Soviet navy, are characterized by high efficiency and exceptionally small weight and size characteristics. In addition, compared to analogues, they are more convenient to maintain and, as a rule, are better assembled on site. However, the entire complex of the above advantages in to the fullest manifests itself when these devices operate on non-viscous droplet liquids, to ensure heat exchange between which these devices were created. The reason is that among a significant number of new technical solutions, embedded both in the design and in the manufacturing technology of these devices, there are a number of specific solutions that provide a subtle mechanism for influencing certain layers of moving fluid based on taking into account the peculiarities of the thermophysical properties of such working media. It was of practical interest to develop, on the basis of these heat exchangers, lightweight and compact devices for highly efficient heat removal from the lubricating oil cooling various machines and mechanisms.
For this purpose, Teploobmen LLC carried out work to modify commercially produced TTAI devices, taking into account the specifics of the task. Such a modified heat exchanger, designed to extract heat from the oil-air mixture cooling the compressor, was tested in October 2006. on the test bench of NPA "VNIIkompressormash" as part of a compressor unit.
The tested heat exchanger retained all the main features of heat exchangers of the TTAI family, i.e. This is a shell-and-tube apparatus with a thin-walled body made of high-alloy stainless steel of the austenitic class, in which a highly compact, tightly packed tube bundle, assembled from extra-thin-walled small-diameter pipes (6mm), located along special the way the breakdown was performed. Tube sheets of the bundle, which have a special two-stage seal with pilot holes, are made using special technology from composite materials. The heat transfer tubes of the bundle, also made of high-alloy stainless steel of the austenitic class, but acid-resistant group (due to a different composition and combination of alloying elements), have a special, so-called. “thermodynamically feasible” profile.
The specified design and technological features of TTAI heat exchangers make it possible to obtain the whole complex consumer properties, which favorably distinguish these devices from their analogues and open up broad prospects, both from a technical and economic point of view, for their use for the utilization of secondary energy resources.
Among the main technical differences are the following.
Installing a tube bundle in the housing according to the principle of both floating tube sheets allows not only to remove concerns about possible occurrence thermal stresses in the “body - tube sheet - tube” chain, but also to radically increase the maintainability of the device, because provides the opportunity to maintenance and repair, remove the tube bundle from the housing. This allows, if the need arises, to replace the tube bundle with a new one without dismantling the device, not to mention access for inspection and cleaning of the inter-tube cavity.
The use of a two-stage seal with a system of drainage grooves and guide holes on floating tube sheets ensures not only the guaranteed exclusion of interpenetration of working media in this place (which is especially important in the case of heat extraction from lubricating oils with water or non-freezing coolants), but also functional diagnostics of the condition of the sealing elements, which allows you to plan their replacement, avoiding an emergency shutdown.
Thanks to the special profile of the heat transfer tubes, not only an accelerated increase in heat transfer coefficients compared to an increase in hydraulic resistance is achieved, but also, under known conditions, a self-cleaning effect. The expediency of an accelerated increase in thermal efficiency is obvious, but the presence of the accompanying self-cleaning effect is a very significant factor, because During operation, the requirements for coolant are often not met, as a result of which various deposits accumulate on the heat transfer surfaces, reducing the efficiency of heat removal, which negatively affects both the operation of the oil-cooled mechanism and the consumers of secondary energy resources.
But one of the most significant advantages of TTAI devices is their insignificant weight-dimensional characteristics compared to analogues, which is achieved due to the mutual influence and complementarity of a number of the above technical features.
Unfortunately, the use of commercially produced TTAI heat exchangers to solve the problem of selecting low-potential heat from a viscous oil-air mixture could not give the necessary results due to the possibility of bypass oil currents and the resulting reduction in the thermal efficiency of the device. This led to the implementation of modifications that were supposed to solve the problem of ensuring an almost pure transverse flow of cooled oil around the tubes of the bundle while maintaining the hydraulic resistance of the oil cavity of the heat exchanger within fairly rigid, limited limits for viscous media. As permissible upper limit The resistance value was taken to be 10 m.w.s., which is more consistent with devices operating on non-viscous media, however, a higher value of hydraulic resistance can make waste heat recovery economically unfeasible, because An increase in heat exchanger resistance leads to an increase in power spent on driving the oil pump.
During the revision, two new fundamentally important decisions were made:
It was decided to group the tubes of the tube bundle in the central part of the body, leaving free passages for the flow of oil from one compartment to another;
It was decided to make the heat exchanger body composite of sections, the length of which is equal to the distance between the partitions of the inter-tube space, and the partitions themselves should be made with a completely closed peripheral cylindrical surface, on which elastic sealing gaskets pressed by the sections of the body rest.
The grouping of heat transfer tubes in the central part (see Fig. 1), on the one hand, makes it possible to reduce the hydraulic resistance of the oil cavity of the cooler by reducing the speed of oil movement in one of the narrowest sections, in which the flow is also turned by 180 o and , on the other hand, excludes from the heat exchange process (and thereby eliminates the need to take into account when performing calculations) tubes that would flow around the oil flow at an angle of attack different from the direct one, and also varying from row to row.
The device shown in Fig. 2 during full-scale tests at the test bench of NPASC "VNIIkompressormash" as part of a compressor unit showed the actual results shown in Table 1.
Table 1
Analysis of these results shows that the modified TTAI apparatus fully meets the requirements for efficient heat removal from a high-viscosity oil-air mixture.
However, it is obvious that the technical advantages of the modified TTAI heat exchanger, despite their attractiveness, cannot be the main goal of creating such a device. The main goal is to create a compact (in order to ensure the possibility of placement at sites where the installation of an appropriate heat exchanger was not previously planned) and relatively inexpensive apparatus (so that the energy gain from the use of secondary resources is not offset by the costs of purchasing and installing a heat exchanger). To analyze these characteristics, a comparison was made of the described heat exchanger with analogues. To carry out such a comparison, Table 2 shows the weight and price characteristics of the three options:
Plate heat exchanger manufactured in Ukraine;
Russian-made shell-and-tube apparatus;
The heat exchanger considered in this article is from the TTAI family.
table 2
It should be noted that the devices given in Table 2 are compared for identical thermal conditions, and it must be borne in mind that if the thermal characteristics of the TTAI device were obtained during full-scale tests, then for the devices of the other two positions one must rely on their design characteristics reported by the manufacturers (as experience shows, actual characteristics are often inferior to calculated ones).
Currently, work is being carried out to create a standard-size range of modified TTAI heat exchangers designed to remove waste heat from high-viscosity coolants. Completing this work will eliminate the last objective obstacle on a way widespread use secondary energy resources in the form of waste heat from high-viscosity liquids that cool operating machines and mechanisms.
Heat recovery systems for electricity generation.
This technology makes it possible to use the (extra) heat to be utilized to produce electricity.
This is a thermal electric generator whose operating principle uses the Organic Rankine Cycle (ORC).
The main element of this thermal electric generator is the ORC turbine. Operating principle, physical basis and aspects of the application of this technology are well described in the article by G.V. Belov. and Dorokhova M.A. (MSTU named after N.E. Bauman), which is available for review on our website.
Electricity generation systems based on the Organic Rankine Cycle can be successfully used in many cases where it is necessary to utilize excess heat generated as a result of the production activities of an enterprise, for example:
Heat recovery when burning plant biomass;
Heat recovery from burning wood waste from sawmills;
Utilization of excess heat from an industrial enterprise;
Utilization of heat received by solar collectors;
Utilization of “excess” heat from traditional and cogeneration boiler houses (especially in the summer)
We offer specific engineering solution, design and supply of appropriate equipment for the implementation of this technology at your enterprise, taking into account your specific conditions and features of the project.
Receiving or using heat is always associated with the problem of releasing unused part of the heat into the atmosphere. For example, at some chemical plants the temperature of exhaust gases exceeds - 800C. IN currently boiler houses are used on gaseous, liquid and solid (wood, coal, wood chips, husks, etc.) fuel, where the outlet temperature is 110C and higher, depending on the efficiency of the boiler.
Boiler houses operating on peat, husks, wood waste, biofuels, fuel oil and other recyclable fuels
Cement, chemical, pharmaceutical, waste incineration plants
As a rule, in energy-intensive enterprises, part of the thermal energy is used, if possible, to provide heat to both buildings and structures of the enterprise itself located nearby settlements. However, it is enough a large number of heat is released into the atmosphere or utilized through cooling towers of various designs.
Cooling towers
Using the suggested modern technologies, recycled thermal emissions can be converted into electricity. In this case, the enterprise can significantly reduce energy costs, thereby reducing the cost of production. When generating heat by burning various kinds waste - wood chips, husks, lignin, household, industrial waste etc. The output is fairly low-potential heat - no more than +300C. However, this is sufficient for using electric generators on ORC turbines. In this case, the most effective generators are those using the organic Rankine cycle, the diagram of which is shown in Figure No. 1.
In short, the principle of using heat is as follows. Inside the sealed circuit there is, for example, R-134 refrigerant, the same as in an industrial air conditioner. When heated external source heat with the help of a heat exchanger separating the medium, the liquid refrigerant boils and turns into gas. The gas expands and rushes into the turbine. Passing through the turbine and giving up its thermal energy, the gas enters the condenser (cooler), where it condenses, turning into liquid. The pump supplies the liquid back to the heating zone. The gas passing through the turbine spins it and the rotational energy of the turbine is converted into electrical energy using an electric generator. Everything is like in a chiller, but in reverse. If in a chiller, with the help of electricity supplied to the compressor motor, the refrigerant (R-134) is compressed and brought to a liquid state with the subsequent production of cold and heat, then in a generator using the Rankine cycle, instead of a compressor there is a turbine, and an electric motor - an electric generator. As for the sizes of installations using the Rankine cycle, as you can see in the photo below, the chiller and ORC generator look very similar and have approximately the same dimensions.
ORC generator with screw turbine Chiller with screw compressor.
ORC generators have different designs, using both gaseous and liquid sources of thermal energy, usually with temperatures above 80C. The long service life of 20 years or more is due to the fact that the turbine operates in a sealed and relatively low-temperature environment with clean gas.
ORC generators do not require maintenance, practically changing the oil and bearings in the turbine and generator every two years.
The resource of the ORC generator exceeds 100,000 hours or more.
The only drawback of the ORC generator is its low electrical efficiency, which ranges from 8-25%. However, the overall efficiency (electricity + heat generation) reaches 85% or more.
But if you look from a practical point of view, for example: a wood chip heat generator with a thermal power of 1000 kW will provide the generation of 100 kW of electricity and about 680 kW of hot water with a temperature of 90/70C and above. This will allow powering all electric pumps, control systems, lighting, etc. Thus, it is practically possible to avoid supplying additional electricity from the outside.
Also, if, instead of a waste heat boiler, an ORC generator is installed on the exhaust of a gas piston cogeneration plant with an electrical power of 1000 kW, then the overall electrical efficiency will reach 38+10=48%, while maintaining the thermal efficiency - about 50%.
ORC generators are manufactured in many countries around the world. Our company is ready to offer you the implementation of this technology on a turnkey basis (design, supply, installation, commissioning, service and post-warranty service), for the most successful solution of energy efficiency problems for your enterprise, residential complex, etc.
We present an exclusive patented heat recovery system. Heating system and hot water supply for free at any time of the year!
It's hard to imagine the world modern man without electricity, water supply systems, heating and air conditioning. The cost of energy resources is constantly growing, and the issue of their effective use. Thermal energy recovery technologies are increasingly used at facilities for various purposes: from industrial production to public areas. This is due to the shortage and high cost of primary energy resources. Refrigeration systems in buildings, such as supermarkets or large refrigeration centers, use large amounts of energy to produce cold. At the same time, they also generate a significant amount of heat. This thermal energy is generated by the process of condensation of refrigerant gas. In conventional refrigeration units, it is released to the surrounding air using condenser units and is not used at all.
The purpose of creating such a system was to ensure 100% return of heat for heating and hot water supply, released during condensation of refrigerant vapors, into the room without negative consequences for operating modes of refrigeration equipment.
Today on Russian market There are no analogues in price, performance, versatility and ease of use. In addition, CTS is several times cheaper than existing analogues.
It is important to note that the installation of the RTS is very simple and can be carried out by any contractor involved in the installation of refrigeration equipment. More than half of the installations of the control system took place at work sites and took no more than 5-10 days.
Arguments in favor of the system:
The system is affordable! Its cost relative to other solutions is two to three times lower, given that it is completely independent - its own circuits, its own heat exchangers, its own automation. For an average store with 7-11 units of refrigeration equipment, the estimated cost of a turnkey system is 400-700 thousand rubles, and the payback will be 1.5-2.5 years. Almost any store or other owner of refrigeration equipment can afford to install a RTS.
Efficiency. The system allows you to shoot maximum amount heat, limited only by the performance of the compressors. If the performance of the fan coil units is sufficient, 100% of the condensation heat will enter the room. Compared to other recovery systems, the efficiency has more than doubled.
The ability to work with any refrigerant (R22, R404a, R407c, R134a, etc.) is achieved by adjusting the pressure regulators and direct heat removal.
Versatility. The system can be easily implemented on almost any refrigeration machines operating on freon: low-temperature, medium-temperature, air conditioners, chillers, etc. There are no performance restrictions. Together with heating, you can heat any medium, for example DHW.
The heat recovery system (HRS) is ideal solution For trading platforms with external cold. Most of After the implementation of UTS, customers refuse central heating.
Cold start. Proper design of the system, adjustment of automation and regulators make it possible to eliminate the presence of freon in the condenser and other heat exchangers on the discharge line.
Ease of use and regulation. The operation of the heating system does not depend on the number of operating or idle fan coils; each fan coil can be adjusted to its own temperature regime.
The recycling system for stores with remote refrigeration is constructed as follows:
A recycling module is installed in the compressor room (engine room of the store), next to the refrigeration machine. Its function is to distribute the flow of hot gas between indoor fan coil units and a remote condenser. Support required pressure in refrigeration circuits. In simple words, if the performance of the fan coil units is sufficient, then 100% of the hot gas will pass through their heat exchange part, if the performance is not sufficient (for example: several fan coil units are turned off or there is already heat) part of the heat from the hot gas will be utilized outside bypassing the heating circuit, but only as much as necessary.
In the heated room, special-design cabinet fan coil units are installed:
The function of fan coils is to transfer heat from hot gas into the room. Installed instead of or together with central heating radiators. The fan coil heat exchanger is made in accordance with all refrigeration laws. Specially designed for hot gas. Pressure testing of the heat exchanger 35 bar (3.5 MPa). Versatility. Can be mounted on a wall, ceiling, and even placed on commercial equipment (for example, on a refrigerated cabinet). The fan coil unit has a control panel with which the required temperature is set, upon reaching which it will turn off:
In our experience, when the recycling system is started, the temperature in the room rises by 10-15 degrees Celsius. The lion's share of properties refuse central heating. An electric curtain at the entrance + a recycling system gives +22 degrees Celsius in a well-insulated room all year round. Of course, a lot depends on the ratio of the performance of the refrigeration equipment to the area of the room, but in any case, the recovery system will return 100% of the condensation heat to the room. Using the example of the store in question, before installing the recycling system, the temperature in the room was +9 degrees Celsius, 6 hours after launch it was +24 degrees Celsius. Central heating didn't connect.
The payback period, depending on the complexity and configuration, is from 0.5 to 2 years.
TAS Retail provides comprehensive design, supply and installation of heat recovery systems.