JP2007132617A - Drying method for high moisture content combustible - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To resolve a problem in a conventional VRC (vapor recompression) method carrying out condensation to recover latent heat of steam disposed when carrying out drying for burning high water content combustibles, wherein a compressor with a rotating part is used, but since the compressor is soiled by the recovered steam, its maintenance/cleaning is troublesome. <P>SOLUTION: Maintenance/replacement becomes easy by using an ejector instead of the compressor. Moreover, by selecting an amount of steam being a driving medium of the ejector such that a steam amount supplied from the ejector becomes a necessary amount for drying, a structure and performance of the ejector are optimized, and extra steam becomes unnecessary in drying. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for drying / combusting combustibles having a high water content.

Non-patent document 1 discloses a VRC method as a method for drying and burning combustibles having a high water content. This is because the steam generated during drying is boosted by a compressor, thereby increasing the saturation temperature and heating steam, and this is heated and dried by the temperature difference from the saturation temperature of the moisture of the multi-moisture combustible material. This is a method for condensing heating steam and recovering its latent heat.
“Possibility of VRC drying in energy conversion of wet biomass” Journal of the Japan Institute of Energy, Vol. 84, No. 4, 2005, p. 353-358

  The present invention relates to a method for eliminating compressor fouling, which is a disadvantage of this method.

  It is necessary to remove moisture by drying to burn combustibles with high moisture. For drying, there is a method in which steam is used in addition to hot gas to heat the moisture-rich combustible material to evaporate the moisture in the moisture-rich combustible material. The heat balance of one example of the dryer is shown in Table 1 below. Show.

  When drying 1,000 kg of 80% moisture-rich combustible material to 20% moisture, the heat is 1.69 GJ for evaporation of 750 kg of water, and 800 kg of moisture and 200 kg of moisture-rich combustible material is 0.27 for preheating from 25 ° C to 100 ° C. GJ, total heat 1.96GJ is required, and if the efficiency of the dryer is 80%, the heat required for drying is 2.46GJ.

  When the dried moisture-rich combustible material is burned, the higher heat value of the moisture-rich combustible material is 18.8 MJ / kg, the lower heat value is 16.9 MJ / kg, and the generated heat is 3.38 GJ. If the boiler efficiency is 80%, the amount of heat generated in the boiler is 2.70 GJ, so the effective amount of heat available is 0.24 GJ (= 2.70-2.46). In other words, the amount of heat that can be used even after drying and burning a high-moisture combustible material is very small, and incineration is possible.

  This is because, as described above, the amount of heat necessary for the evaporation of moisture in the high-moisture combustible material, that is, the latent heat 1.69GJ is discarded to the atmosphere together with moisture, and this is the amount of heat required for drying 1.96GJ. It reaches 86% (= 1.69 / 1.96).

  In this method of recovering latent heat, as shown in the above-mentioned Non-Patent Document 1, the steam is pressurized by a compressor, thereby increasing the saturation temperature to form a heating steam, and saturating the moisture of the multi-moisture combustible material. There is a method of heating and drying this by a temperature difference from the temperature, condensing the heating steam, and recovering the latent heat.

  This is called the VRC (Vapor Recompression) method. This is because the heat transfer is performed by evaporation and condensation with a large heat transfer coefficient, so there is an advantage that the device is compact. However, since the pressurized steam is obtained from the moisture of a highly moisture flammable material, there is dirt, the compressor In particular, since the rotating part becomes dirty or corroded, there is a drawback that it is difficult to clean and maintain.

  Conventionally, the steam supplied from the boiler to the dryer is heated and dried by the indirect heating method using a dryer, which eventually becomes hot water close to 100 ° C, but is reused because it is not dirty. it can. However, the utility value is low in the form of warm water.

  The present invention improves these drawbacks and provides a VRC process that is resistant to soiling and a system that produces highly useful steam.

  The present invention provides a drying and combustion system that is compact and easy to maintain by using an ejector to increase the pressure of water vapor, thereby eliminating a rotating part. Next, the steam supplied directly from the boiler to the dryer heats and dries the highly-moisture combustible material in an indirect heating mode in the dryer, and eventually becomes hot water close to 100 ° C, which is used as the feed water for the steam boiler. to recover. As a result, the amount of heat recovered from the hot water can be finally changed to steam, and a simple system with high utility value is provided.

  The dried high-moisture combustible material is burned with a steam boiler to obtain steam, which is used as a drive medium for the ejector. The water vapor generated from the high-moisture combustible material in the dryer and pressurized by the ejector and the steam that is the driving medium are used to heat the high-moisture combustible material by indirect heating, condensing into saturated water, and further high-moisture combustible material. The product is cooled to a final temperature close to 100 ° C. Furthermore, if it is used for preheating of a high moisture combustible material, it will be discharged at a low temperature. This water cannot be used because it is usually contaminated with a high moisture combustible material.

  To further simplify the system, do the following: The amount of steam supplied from the steam boiler as the drive medium of the ejector is equal to the amount of heat necessary for drying the multi-moisture combustible material so that the amount of heat of the steam supplied from the ejector to the dryer together with the water vapor generated by drying is equal. You can choose. If it does in this way, the calorie | heat amount (steam) supplied from others will become unnecessary.

  If the drive medium amount of the ejector is reduced, as will be described later, the efficiency of the ejector is improved in calculation, but it is determined that it is not practical.

  In order to burn a high-moisture combustible material with a high water content and recover the heat, it is first necessary to dry. However, conventionally, water vapor generated during the drying has been discarded. However, for example, in the case of a high-moisture combustible material having a moisture content of 80%, the latent heat becomes 86% of the heat amount required for drying. According to the present invention, the latent heat is recovered by pressurizing the water vapor with an ejector, increasing the saturation temperature, and again using it as heating steam for drying, thereby condensing it. Since this condensed saturated water is contaminated by the high moisture combustible material, it is discarded after thorough heat recovery is performed for preheating the high moisture combustible material. Moreover, since the steam from the steam boiler used for drying the multi-moisture combustible material is not contaminated due to indirect heating, it is condensed and becomes saturated water, and then recovered as part of the feed water for the steam boiler. The system of the present invention is simple because only steam is output.

  When drying high-moisture combustible materials with high moisture content, use an ejector to increase the saturated vapor pressure by pressurizing the water vapor generated during drying, and heat it by the temperature difference between the material to be dried and water vapor. The steam condenses and recovers its latent heat, but the amount of steam from the steam boiler that is the drive medium of the ejector is selected so that the amount of heat from the ejector is equal to the amount of heat required for drying, and condensation of the steam for heating The water is cooled by preheating the material to be dried and recovered after recovering the heat. The dried combustible material is burned with a steam boiler to obtain steam. This steam is used as a drive medium for the ejector.

  Examples of the present invention are shown in FIG. 1 and Table 2 below.

  As shown in FIG. 1, the amount of heat of 1.96 GJ (2.46 GJ if the efficiency of the dryer is 80%) is required to dry 1,000 kg of highly flammable combustible material with 80% moisture to 20% moisture. When 0.3MPa, 550kg, 1.50GJ steam is used for the ejector drive medium, 0.1MPa, 100 ℃, 750kg, 2.01GJ steam generated from the dryer is sucked into the ejector, and the pressure is increased to 0.2MPa, 120 ℃. A total of 1,300 kg and 2.96 GJ of steam is the heat source for drying, but considering the loss (η = 0.83%) of the ejector and piping, it becomes 2.46 GJ and can provide the heat required for drying. This steam enters the dryer and heats and dries the high-moisture combustible with a temperature difference of 20 ° C (= 120-100), and the heating steam condenses to become saturated water, and further generates high-moisture combustible or from it. It is cooled to near 100 ° C by steam at 100 ° C. This hot water is dirty and is discarded because it cannot be recovered. This can be further used for preheating of the moisture-rich combustible, and the sensible heat can be recovered (with an indirect heater) and then discarded. However, this is omitted in the system of FIG.

  Steam boilers dry fuel up to 20% and use it as fuel. As shown in Table 3 below, the efficiency of the ejector is better when the amount of steam in the drive medium is small, but the calculation does not take into account losses such as friction and vortex generation in the ejector. Calculated. In practice, the efficiency of the ejector is not expected to exceed 60%. On the other hand, if the ejector area ratio m = F / F1 is too large, mixing of the vapor in the ejector is deteriorated and efficiency is lowered. Considering these, the design of the column surrounded by the thick line in Table 2 seems to be optimal.

  The amount of steam generated in the steam boiler and its calorific value are 0.3MPa, 1,031kg, 2.81GJ, and the steam amount and calorie required for the ejector are 0.3MPa, 550kg, 1.50GJ. The amount of heat is 481kg, 1.31GJ. Thus, the VRC method using an ejector, in particular, the system shown in FIG. 1 is very simple. The surplus heat is obtained in the form of steam, which is quite large at 481kg and 1.31GJ.

  In order to burn combustibles with a lot of moisture, the water must be dried to evaporate, but this water vapor is usually discarded. However, since the latent heat of the water vapor accounts for most of the heat for drying, it is very uneconomical and it is desirable to recover this latent heat. For this reason, when water vapor is cooled and condensed with water, latent heat is recovered in the form of warm water, but the use of warm water is few. In this method of recovering latent heat, the water vapor is boosted with a compressor, the saturation temperature is increased, and it is made into steam for heating. The method of condensing steam and recovering its latent heat is the VRC method, but the compressor, especially its rotating part, is dirty and has the disadvantage that it takes time to clean and replace.

  The present invention provides a way to eliminate this drawback by using an ejector instead of a compressor. The ejector is easy to clean and replace. Since the drying / condensation process is performed by evaporation / condensation with very good heat transfer on both sides of the heat transfer surface, the dryer becomes smaller.

  In addition, the amount of steam supplied from the steam boiler as the drive medium of the ejector is set so that the amount of heat of steam supplied from the ejector to the dryer together with the water vapor generated by drying becomes equal to the amount of heat necessary for drying the multi-moisture combustible material. If it is selected, the amount of heat (steam) supplied from others is not necessary, the system can be simplified, and the structure and efficiency of the ejector are also optimized.

  According to this system, a large amount of the heat of the high-moisture combustible material that has been discarded in the past can be recovered in the form of steam, and the system and the apparatus become compact.

It is a system | strain of 1 Example of this invention, and the pressure and flow volume of a substance, and calorie | heat amount.

Explanation of symbols

1 Steam boiler 2 Dryer 3 Ejector

Claims (3)

  A drying method such as a multi-moisture combustible material in which water vapor generated during drying is pressurized by an ejector to increase the saturation temperature, the water vapor is condensed by a heated object, and the latent heat of the water vapor is recovered.   The heat source of the dryer according to claim 1 is steam emitted from the ejector and steam of another system supplied from a steam boiler. The former indirectly heats the object to be heated, condenses it with the object to be heated, and further preheats the object to be heated. The latter is dried after being cooled by using the latter, the latter is dried by indirect heating, and after being condensed, it returns to the steam boiler as feed water to recover the heat of steam and water vapor used for drying. Drying method for things. A drying method for a multi-moisture combustible material, wherein the amount of steam from a steam boiler as a drive medium of the ejector is determined so that only the steam supplied from the ejector is sufficient as a heat source of the dryer of claim 2 .

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