RU2581264C2 - Method and device for drying and heat treatment - Google Patents

Abstract

FIELD: energy.

SUBSTANCE: invention relates to thermal processing of moist materials in particular organic materials to drying in preparation for combustion and/or waste treatment. In power engineering drying of wet fuel increases efficiency of its use. Method and apparatus intensive drying and heat treatment of wet material with superheated steam at elevated pressure, which is generated due to moisture evaporated in heat exchanger and external heat is used for further overheating of steam turbine drive operating on Rankine cycle, to produce electricity or mechanical work. To improve steam parameters that determine thermodynamic efficiency of drying device with production of useful work, proposed is a twin-drying chamber design with an internal heat-resistant alloy casing can withstand high temperature steam at a relatively low pressure difference between inside and outside, and outer casing to withstand high internal pressures at high dimensions of chamber, but under normal operating conditions with insulation installed between hulls, optionally with neutral gas pressurisation therebetween. Provided is collection of resinous fractions, released from many organic materials during high-temperature treatment. Furthermore, disclosed is method that enables to eliminate in steam for turbine undesirable contamination of solid or liquid phase, realised due to that steam carrying energy to turbine after its withdrawal from drying chamber and heat fed to separating heat exchanger to generate by steam heat exchange pure water for turbine. Reliability of entire system is significantly improved.

EFFECT: disclosed energy-saving technology is suitable not only for intensive drying of combustible materials, thermal processing of raw materials from tar fractions, but also provides complete protection against unpleasant atmosphere gases by drying and sterilisation of sewage.

3 cl, 2 dwg

Description

The invention relates to the field of heat treatment of wet materials, in particular to drying of organic raw materials in preparation for incineration and / or processing of waste. In the energy sector, drying wet fuel improves the efficiency of its use.

Intensive drying, as a rule, is carried out due to the low potential heat taken from the output of power plants and spent on moisture evaporation. It is introduced into the drying device with a stream of gas or steam as a coolant in direct contact with wet material, or by means of heating surfaces that heat the contents of the working chamber. It is the rate of heat transfer to the wet material that determines the intensity of the drying process. In the process of heat transfer, air, as a coolant, is significantly inferior to steam, especially at a vapor pressure above atmospheric. A known method of heat treatment, such as steam sterilization under pressure, and drying the material with the same steam, which is in an overheated state when the pressure is released [Patent application US 2008005923 (A1). Apparatus and method for drying the instrument with superheated steam]. But in this drying method, together with steam leakage during pressure relief, a significant heat of phase transition of moisture is lost. A drying method is also known, in which the heat of the phase transition during moisture condensation is returned to the heating steam when using a heat pump [Patent EP 0063708. The process of economical drying and apparatus for its implementation]. However, the temperature head created between the heating and heated media is determined by the amount of mechanical work supplied, and therefore this drying method, if necessary, intensifies it becomes energetically inefficient, that is, too energy-intensive, although it can be useful for gentle drying under vacuum at low temperature. Since the process in the method is carried out in isolation from the environment, volatile, unpleasant odors and other undesirable substances released during drying can be removed by vapor condensation, which is safe for the environment. Finally, a drying method is known [US Pat. No. 3,946,495. Method and apparatus for drying wet household waste and sewage sludge], in which this process is carried out in a multi-zone vertical chamber with direct contact of a downward flow of wet material and an upward flow of steam, which is superheated at the inlet and cooled to the saturation state at the outlet, followed by compression compressor and heat extraction with boiler feed water, while the part of the steam flow corresponding to the moisture of the raw materials introduced into the device is directed to the steam superheating line and then to the turbine, which ensures Nergy system operation. The burning of the drained mass ensures the generation of steam in the boiler for drying and energy production by the turbine, and the condensation of the steam behind the turbine is used to generate heat at the distillation plant and produce fresh water. Thus, the described drying method is more effective than all of the above. It is adopted as a prototype. However, even in this invention all the possibilities of improvement are not used. We note, first of all, the extremely limited size of the region of interaction of superheated steam with wet material. This circumstance, obviously, is due to the large pressure drop in the drying chamber adopted in the patent when heating steam is circulated, and the need to use an energy-intensive compressor to compress wet steam. Energy costs could be reduced by drying in a substantially larger chamber and using traditional means of increasing the surface of interaction of the wet material with the coolant, in particular in systems with a conveyor belt [www.dorset.nu Dorset Green Machines B.V. Weverij 26 7122MS Aalten the Netherlands] or as in multi-hearth furnaces. Further, a small amount of steam pressure in the boiler of the prototype limits the efficiency of the steam-power cycle (turbine). This characteristic of this method could be improved by improving the design of the drying chamber. And the presence of contaminants, which are also introduced into the vapor during evaporation of the moisture of the material, and with the steam can be introduced into the turbine, should be considered as threatening its reliability.

The aim of the invention is to eliminate these disadvantages, improving the drying method and design of the device.

To achieve this goal, it is proposed:

1. The method of drying and heat treatment, based on the direct interaction of superheated steam with increased parameters with wet material in the drying chamber, as a result of which the moisture of the material evaporates, the steam is cooled, with the help of a circulation agent heating steam along with the vapor of the evaporated moisture is removed to the heating heat exchanger, and then superheated steam is again used in the drying chamber, while removing part of the steam equal to the amount of evaporated moisture of the material to overheat to drive the steam turbine, with the difference between the proposed method ba, that pure steam is sent to the turbine, obtained in a separation heat exchanger by heating pure water due to the heat of cooling and condensation of superheated steam removed from the drying chamber to drive the turbine, with the removal of non-condensable components for afterburning, or for use as a useful product, if it is possible.

2. A drying and heat treatment device comprising a drying and heat treatment chamber with high pressure superheated steam, with a wet material input and transport system during the drying process, and a dried material output system, also containing a steam circulation circuit with a steam flow inducer and a heat exchanger for heating it, which it is connected from the inlet of the flow inducer to the steam extraction in the chamber in the area of the wet material inlet, and behind the heat exchanger - from the outlet of the dried material from the chamber, and the steam outlet is also connected there, pre assigned to drive the steam turbine to its heat exchanger overheating before being fed to the steam turbine drive, with the difference of the proposed drying device that the steam line from the drying chamber and its heat exchanger to the turbine is connected to the heating side of the separation heat exchanger, where the steam cools and condenses, giving off heat to generate steam on the heated side of the heat exchanger, where clean water is supplied, and pure steam from the outlet of this side of the heat exchanger is connected by a steam line to the turbine.

In addition, to increase the temperature and pressure in the body of the drying chamber, necessary to increase the thermal efficiency steam-turbine cycle, it is proposed:

3. The drying and heat treatment device according to claim 2, wherein the drying chamber body is complex: the inner one is made of steel having high heat resistance calculated for the maximum drying temperature, but without a large pressure drop across the inner case, which is separated by a layer of thermal insulation from external power casing, designed for maximum pressure in the drying chamber and operating at a limited temperature, and for the removal of resins that may be released in the inner casing of the chamber during high-temperature processing x material in its lower part taken controlled discharge orifice and all the input / output media into / from the chamber connected device acting as gateways.

The technical nature and principle of operation of the invention are illustrated in FIG. 1 and FIG. 2. The principle of operation is explained by Ts - diagram of a somewhat idealized process of energy-saving drying for moisture vapor. In FIG. 1 shows the region of two-phase states for water and water vapor. The moisture of the material is first heated during drying (the process is described by the left boundary curve), and at a temperature corresponding to saturation at a given pressure in the drying chamber, the moisture begins to evaporate in a near-isothermal process until all moisture passes into steam (on the right boundary curve), after which the temperature rises with constant heat capacity. The enthalpy (heat content) of the steam in this case is continuously increasing, and upon reaching the maximum temperature level the vaporized vapor is transferred to the turbine, where it has a relatively high efficiency acquired vapor enthalpy will be turned into work. Therefore, unlike other technologies, this drying with the production of useful work that compensates for heat costs can be considered energy-saving. As a justification for this statement, we present the results of the calculation of the efficiency turning the drying energy into a turbine operation. Example: the drying pressure is 1.5 MPa, the upper steam temperature is 600 ° C, the pressure and temperature behind the turbine is 0.01 MPa - 75 ° C, efficiency turbines - 0.88, efficiency conversion of steam energy into electricity - 0.275. These indicators are good even for power plants that use low-quality fuels or utilize thermal discharges, and in this case this energy is given simply as an application to intensive drying. The easiest way to increase energy during drying is to increase the pressure in the chamber. But problems may arise in its structural strength, reliability, cost. As a solution to these problems, it is proposed to use the double-shell design of the drying chamber with separation of the functions of heat resistance and mechanical strength, which is discussed in Section 3.

But the steam is probably contaminated by particles of the material to be drained during evaporation, and the turbine is a very critical apparatus for the purity of the steam. Therefore, the proposed technology and its installation scheme provides for the separation of material and energy flows using a separation heat exchanger. The moisture vapor of the material according to this invention does not directly enter the turbine, it exchanges energy with clean water, moreover, the heat exchange processes on high pressure steam, especially in the zone of condensation of moisture vapor and boiling water, are characterized by extremely high intensity, and the temperature difference between the heating and heated media can be no more than 15-20 ° C. This means that in the Ts diagram, the line of the process of steam formation from pure water in the indicated heat exchanger lies only slightly lower in temperature than the moisture vaporization line of the material during drying, the areas under these curves characterizing the supplied heat are almost the same, that is, at the same mass flow rate of these steam flows, the upper pressure level and the maximum temperature of the described processes are almost the same. When generating steam, we must monitor the energy balance in terms of temperature and pressure and adjust the flow rate following the variations in the input thermal power or the steam flow rate to the turbine for different circumstances. These are standard procedures for monitoring any power plant. You should not directly regulate the pressure, except in emergency situations. All devices with steam, heating heat exchangers, loading the turbine in accordance with the general rules of this kind of work are carried out according to the prescribed rules and established means, including automation. We also note that the transport of incompressible media (supply of material for drying, water to the heat exchanger, condensate outlet) is carried out with a certain margin in the drive by pressure, which is usually regulated by its reduction as necessary. We are constantly faced with this, even using water from the water supply.

The installation diagram that implements the drying and heat treatment of wet material described above with the production of mechanical work or electricity according to the method of claim 1 is presented in FIG. 2. Characteristic standard elements are indicated here that do not require explanation for heat and power specialists. The notation in FIG. 2: 1 - drying chamber; 2 - input device for wet material under pressure (auger or lock); 3 - flow rate inducer (gas blower, fan); 4 - heat exchanger-superheater (superheater); 5 - removal of heating gases; 6 - input heating gas; 7 - conclusion of the dried material or mass (auger, sluice); 8 - heat engine (steam turbine); 9 - produced mechanical work or electricity; 10 - steam condenser; 11 - removal of non-condensable gases; 12 - tap to drain the disinfected sterilization of moisture of the material; 13 - separation heat exchanger; 14 - capacitor in a clean water circuit; 15 - feed water pump. The clean water circuit is closed and requires virtually no recharge.

It is necessary to emphasize the very important differences introduced by the feature of the chosen method of evaporation of moisture from the material and steam production, in the work of the corresponding elements. In the circuit according to claim 2, in addition to the separation heat exchanger, there are no elements where the heating surfaces come into contact with wet masses or the liquid phase, which would make it possible to form scale, which negatively affects the heat transfer and structural stability. It is also recommended that the temperature difference between the heating steam and the saturation temperature of the moisture in the drying chamber be kept high, since this allows you to intensify the heat transfer from steam to the wet material (unlike the prototype, where the steam is cooled to a state of saturation, that is, almost to zero drying efficiency).

Finally, we indicate that the by-product of the new drying technology can be resins, the condensate of which can be released in the drying chamber in the form of a liquid phase draining to the bottom at a temperature above the boiling point of water, and must be collected (not shown in the diagram), and even a short one is possible to remove the resins excess temperature in the chamber. Since in most processes of the subsequent use of dried material, for example, biofuel, by gasification, resins are undesirable, modes with their special condensation are not provided. However, some products of thermal processing of wet raw materials (resins, oil fractions, etc.) could be of economic interest, and a corresponding modernization of the technology is possible, although it is not discussed in the application.

Finally, we consider the only non-standard element in the entire proposed installation - this is the drying chamber itself. It may be necessary to have a drying chamber of large dimensions, and at a pressure of more than 1 MPa at temperatures of 300-500 ° C, this device will be unreasonably expensive. An alternative to such a direct technical solution may be a design with separation of functions at high temperature and ensuring strength at high pressure. For this, the internal, “hot” part of the structure is made in the form of a relatively thin, but gas-tight shell made of heat-resistant steel, based on effective thermal insulation, for example, in the form of a backfill, enclosed in a power housing made of structural steel for normal operating conditions. Since the behavior of the inner shell may be little predictable under unstable conditions of thermomechanical loads, it is recommended to unload it by supplying a neutral gas between the inner and outer layers under a pressure equal to the pressure inside the drying chamber. It is desirable to automatically maintain this equality of pressures during operation of the device. Since the internal hot wall of the chamber cannot have a temperature lower than the heat carrier, i.e., superheated steam for drying, the resins should not settle on it, but only drain into the collector located below, from where they are discharged in the liquid phase, opening the drain hole only for draining liquid phase. As with condensate drainage from a separation heat exchanger, this operation is simple and could be performed manually, but there are various automated devices for such purposes, however, their consideration is not the subject of this invention.

As for the drying chamber configurations, a number of successful solutions are known for this, for example, multi-deck constructions (vertical arrangement) or horizontal constructions with tedding devices and moving raw materials in countercurrent with a heat carrier, but options with rotation of furnaces for the proposed concept do not seem suitable.

The last remark concerns the selection of a heat source for the operation of the drying device. It is proposed for this to use the heat of combustion products, including from the combustion of the drying product, and part of the heat behind the turbine. In some cases, other external sources may be used, if available. But their selection and optimization does not directly affect the subject of this patenting.

The only unaffected issue of the operation of the presented device is the procedure for its output to the calculated mode. Obviously, for this it is necessary to ensure the production of steam to launch the entire system.

Claims (3)

1. The method of drying and heat treatment, based on the direct interaction of superheated steam of increased parameters with wet material in the drying chamber, as a result of which the moisture of the material evaporates, the steam is cooled, with the help of a circulator, the heating steam together with the vapor of evaporated moisture is removed to the overheating heat exchanger, and then superheated steam is again used in the drying chamber, while diverting part of the steam equal to the amount of evaporated moisture of the material to overheat to drive the steam turbine, characterized in that ravlyaetsya clean steam generated in the heat exchanger separating clean water by the heat of cooling and condensation of the superheated vapor withdrawn from the drying chamber to drive the turbine, while a tap on the post-combustion of non-condensable components, or for use as a useful product, if possible. 2. A drying and heat treatment device comprising a drying and heat treatment chamber with high pressure superheated steam, with input and transport devices of wet material during the drying process, and output of the dried material, also containing a steam circulation circuit with a steam flow inducer and its overheating heat exchanger, which connected from the inlet of the flow inducer to the steam extraction in the chamber in the area of the wet material inlet, and behind the heat exchanger - from the outlet of the dried material from the chamber, and the steam outlet is connected there, designed to drive a steam turbine to a heat exchanger overheating before being fed to a steam turbine drive, characterized in that the steam line from the drying chamber and its overheating heat exchanger to the turbine is connected to the heating side of the separation heat exchanger, where the steam cools and condenses, giving off heat to generate steam on the heated side of the separation heat exchanger, where clean water is supplied, and the clean steam from the outlet of this side of the separation heat exchanger is connected by a steam line to the turbine. 3. The drying and heat treatment device according to claim 2, wherein the drying chamber body is complex: the inner one is made of steel having high heat resistance calculated for the maximum drying temperature, but without a large pressure drop across the inner case, which is separated by a layer of thermal insulation from external power casing, designed for maximum pressure in the drying chamber, and operating at a limited temperature, and for the removal of resins that can be released in the inner casing of the chamber during high-temperature processing of their materials, in its lower part there is a hole for controlled discharge, and devices acting as gateways are connected to all inputs / outputs of media to / from the camera.

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