JPS6186999A - Method and device for indirectly drying sludge, particularly, waste-water sludge - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of Application The present invention provides a method for dewatering sludge, optionally mechanically.
Or for indirectly drying sludge by preheating.
IP! fK relates to a method and apparatus for drying wastewater sludge.

BACKGROUND OF THE INVENTION A series of essentially one-step drying methods for wastewater sludge, which are divided into two process categories, namely methods with direct drying and methods with indirect drying, is known. ing.

The disadvantage of the direct drying method is that the drying insecticidal steam mixes with the large volume of flue used for drying and thus disposes of the waste gas, which is expensive and time consuming. Even post-combustion is necessary. In this drying process, it may occur that during after-combustion, for example, the energy advantages achieved in the drying process itself are no longer available. When the waste gas generated in the drying process is cleaned,
This is accompanied by the drawback that, despite the cleaning process, odor is emitted that pollutes the environment.

In the known method with an indirect drying process, heating is carried out using steam or other thermally conductive media, such as heated oil, in which case the steam is drawn in at ambient pressure and then condensed. be done. This process has to be carried out at very high energy levels and therefore has associated energy management drawbacks.

Since in many sludge combustions the flue gas is delivered to a steam boiler or air preheater at a temperature of 100-300C, it is often not economically advantageous to recover more energy. This is because the energy recovered in this way has a relatively low temperature level. This is particularly because, when the flue gas is at pressure, a significant proportion of the energy recovered can only be obtained by condensing water vapor below the temperature of the SSC. This energy is often used for central heating or for producing hot water.

Furthermore, it has been proposed to utilize this energy for heat pumps. In this case, the use of heat pumps is particularly expensive, as it consumes a considerable amount of electrical energy.

OBJECT OF THE INVENTION The object of the invention is to create a method and a device in the manner described at the outset, making it possible to utilize the above-mentioned still low level of energy for the drying process.

Means for solving the problem In the method of the type described at the beginning, the above problem is achieved by drying on the sludge side at low pressure, in which case the low pressure is sucked in by an injection condenser to draw steam (Brueden). This can be solved by making it occur more frequently.

Furthermore, the apparatus for carrying out the above-mentioned method of the invention is characterized, in particular in the case of a one-stage method version, by a mechanical sludge pre-dryer, for example in the direction of gravity. , a barometrically regulated injection condenser and at least one indirect sludge dryer with a gas-tightly encapsulated sludge chamber, in which case a gas dome of the sludge chamber draws in the steam. The injection condenser is connected to the injection condenser via a conduit for the injection.

action The method mode described above has significant advantages.

The essential advantage is that, by drying at low pressure, it is possible to heat the dryer, here an injection condenser, for example, with the waste steam. The generation of low pressure by the injection condenser by absorbing the steam generated by the dryer has the significant advantage that the steam is immediately condensed on the spot and therefore does not pollute the environment. . The small portion that is not condensed is sucked up by a blower and supplied to the combustion section provided at the rear.

According to another embodiment of the invention, the low pressure is set in the pressure range below KO03 bar absolute.

For example, the steam in the injection condenser is lJ at an average temperature of 40C!
When compressed, a pressure is created on the sludge side in the dryer equal to the pressure loss in the supply line between these two apparatus units. This results in a boiling temperature on the sludge side in the dryer, for example 45-50 C, which is slightly higher than the temperature in the injection condenser.

According to another embodiment of the invention, the sludge chamber of the dryer is hermetically encapsulated, in particular in which the steam is installed in a barometric manner and the injection condensate is subjected to the action of coarse sludge, wastewater or cooling water. It is configured so that it is absorbed by the vessel and condensed on the spot. The mixing condenser is installed, for example, 10 m above the bottom, in order to generate the necessary low pressure without the use of other auxiliary means under the action of coarse sludge or wastewater. The uncondensed material is absorbed by a vacuum blower, and its pressure rise is gradually reduced.

When compared with the conventional method, in the conventional method a temperature difference of 64 C occurs when heating the dryer with temperature steam of, for example, 7 bar and 1640 °C and an ambient pressure running on the sludge side, while condensation The boiling temperature inside the vessel is 45C and 1.5
65C when the dryer is heated with a crowbar and 110C steam
It was found that a temperature difference of . and n, the heat exchange surfaces are practically the same, in which case the advantage of the present invention is that it is possible to use inexpensive waste steam in this process step, whereas the process according to the known technology The steps require the use of expensive energy.

According to another embodiment according to the invention, the drying is carried out in two working stages, in the first stage a low pressure is applied on the sludge side as already stated in claim 1 and in the second stage Work is carried out by applying normal pressure or super pressurization on the sludge side. This method constitutes another invention in the book. This is because the sludge drying known up to now was essentially carried out in one working step. It has been found that the two working steps in the claimed method form provide other significant advantages.

It is advantageous to carry out the heating in the first stage using a heat carrier, for example heat transfer oil or steam, in which case this heat carrier is heated in a heat exchanger with the steam coming from the second working stage.

The advantage of using an intermediate heat carrier is that it is possible to use heating surfaces that are difficult to access in heat exchangers or dryers. This is because this heating surface is not contaminated on the heating jacket side by condensation of steam coming from the second working stage. If the heating surface is dirty, heat exchange will inevitably deteriorate.

In a particularly advantageous embodiment of the invention, a brominated chlorinated hydrocarbon, for example trifluorotrichloroethane (C2Cl3F5), is used as heat transfer medium for indirect drying.

This heat-conducting medium is, for example, 1,2 at a temperature of 55C.
It has a steam pressure of 85 bar, ie slightly above ambient pressure, and is therefore well suited for %.

According to a further development of the invention, a stirring gas, which is obtained by sludge combustion in an air preheater and which is passed through a steam boiler, is used to evaporate the heat transfer medium.

The advantages of this have already been mentioned above.

It is advantageous to cool the flue gas in a heat exchanger, in particular a finned tube heat exchanger, to a temperature below about 60 C relative to the heat transfer medium, in which case according to the invention the heat transfer medium is It is evaporated in a heat exchanger at 50-80C5, preferably 55-60C.

These values are adapted to the energy behavior occurring in combustion devices. In order to obtain sufficiently good drying values for sludge drying, in the present invention a vacuum of about 0.04 to 0.3 bar absolute is applied with the saturated steam of the heat transfer medium leaving the heat exchanger. The sludge dryer is heated.

Under such low vacuum conditions, the boiling temperature of sludge water is about 28-45C. Along with this, approximately 20~SOC
temperature drop is used for drying. The vacuum is maintained by condensing the resulting steam, for example in an injection condenser cooled with purified waste water. Inert gas is sucked in by a vacuum pump.

In the process according to the invention, trifluorotrichloroethane is added at a temperature approximately equal to the temperature at which evaporation also takes place.
It is advantageous to bring it to iiipm in a dryer. In this case, the pressure loss in the working system is negligible. That is, as is the case when using a heat pump,
It is not necessary to use a compressor.

If other operating conditions are selected, for example when the coolant is used at high boiling pressure, this coolant is superheated and discharged, e.g. via a turbine, to generate a flow and then only dried. Used to heat the machine.

In this case, the method according to the invention is not limited to working in the temperature ranges mentioned above. In this method, the limit values vary depending on the working conditions, but the above temperature range U is advantageous in that the energy currently unused and dissipated into the surroundings can be used, for example, for sludge drying. It is. Of course, it is also possible to perform heating in other drying steps using this method.

If a two-stage method is preferred, the above-described device according to the invention has, in addition to the above-mentioned features, a second indirect sludge dryer downstream of the first indirect sludge dryer. 1
It is characterized in that a heat exchanger is provided which is heated by the steam coming from the second sludge dryer for heating the heat carrier of the first sludge dryer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus according to the exemplary embodiment illustrated in FIG. suitable for implementation.

The injection condenser 1 is installed in the manner of a barometer, for example in a cavity indicated by reference numeral 2, 10 m from the ground. This injection condenser is fed with excess sludge. This takes place via the conduits illustrated in the drawing. The outflow pipe 3 of the injection condenser 1 opens into a dip pipe 4 which is provided upright on the ground 2. The wastewater sludge coming from the dip tube 4 is fed to a centrifuge @5, where it is dewatered and subsequently fed via appropriate equipment parts to a first indirectly heated sludge dryer 6.

The sludge dryer 6, whose sludge chamber is important, is hermetically encapsulated.

Via the conduit 7 steam is drawn off from this gas dome and by loading the gas dome of the injection condenser 1. There the steam is condensed.

In a two-stage method, the sludge predried in the sludge dryer 6 is fed to another sludge dryer 8;
There, it is eventually dried and sucked out as dry sludge. The steam passes through the gas dome of the second sludge dryer 8 through a conduit 9
The heat exchanger 107 is loaded, and then the conduit 11
It leaves the device as a condensate.

The heat exchanger 10 heats the heat carrier guided in the circulation system. This circulatory system is indicated by arrow 12 in the drawing. This heat carrier is then transferred to the sludge dryer 6 in this case.
is indirectly heated, while the sludge dryer 8 is indirectly heated, for example by steam.

Elements in the working circuit diagram of the device shown in FIG. 2 that are the same as those shown in the working circuit diagram according to FIG. 1 are designated with the same reference numerals. Of course, to avoid confusion, 1 is added. For example, the arrow indicating the heat carrier circulation system is 12a
shown in the center of the drawing.

The heat carrier circulation system 12a is such that the heat carrier is condensed in the sludge dryer 6a and pumped as a condensate to the pump 131.
C is completely supplied to the heat exchanger 10a, where it is evaporated and then supplied as steam to the sludge drying %6a.

The flue gases necessary for carrying out the evaporation 2 in the evaporator 102L pass through the conduit 14 into the peg and leave this conduit, for example via the schematically illustrated furnace 15.

The sludge flows into the dryer 6a through, for example, 4v16, and leaves the sludge dryer as dried sludge. As a variant of the configuration according to FIG. 1, the device is provided with an oversupply conduit 17 for waste water, sludge or cooling water;
These substances are fed to the injection condenser 1a, which generates a low pressure in the υ sludge dryer 6a.

The working method of the present invention will be explained based on the drawings.

The wastewater sludge, which has a solids content of 1 to 10% TS (substances to be dried), is fed through an injection condenser, 14 centrifuges, a screen belt press (5isbbadpr
essa) etc. to a solids content of 10-35% TS.

This dewatered sludge is fed to a steam or steam heated dryer, such as a thin film evaporator or a disc dryer.

The steam produced in this dryer is condensed in an injection condenser at a temperature of 10C up to 8DC, preferably 10C to 40C. This creates pressure within the dryer on the sludge side. This pressure is higher than the vapor pressure of water at maximum temperature in the injection condenser by the pressure loss in the thread.

The pressure on the sludge side in the dryer corresponds to a boiling temperature of about 25-45C. The dryer is heated with about (0.8 to 2 par) steam or hot carrier oil. Therefore, at least 40
Δt of C occurs.

This Δt is sufficient to achieve sufficient evaporation efficiency.

Steam is generated in a boiler for heating the first working stage, which is heated by condensing the steam coming from the second working stage in a special heat exchanger.

If a heat carrier oil is used instead of steam for drying, this heat carrier oil is heated to a temperature of about 90-120C with the steam coming from the second stage.

The steam coming from the second working stage is placed in a vapor compressor, with approximately the same temperature difference in the first working stage as in the second working stage (if heating is carried out with steam in the first and second process stages). Compressed to 8 degrees resulting.

The pre-dried sludge IL'i coming from the first working stage is approximately 4 to 15 bar in the second working stage, advantageously 6 to 12 bar.
bar steam or about 120 to 520 C, preferably 1
Dry with heat carrier oil at 80-500C.

This method reduces the extraneous energy consumption for sludge drying to about 60%.

Of course, the above-described embodiments of the invention can be modified in many respects without changing the basic idea of the invention. That is, the invention is not limited to the foil making specifically shown and described above. In this case it is also possible to use the same or identically performing device parts. The above pressures and temperatures are given by way of example only.

[Brief explanation of the drawing]

FIG. 1 is a working circuit diagram of a manufacturing device for carrying out the method according to the present invention, and FIG. 2 is a modification of the working circuit diagram of equipment #'i. The symbols in the figure are 1... Injection condenser 2... Ground 3... Outflow pipe 4... Soaking container 5... Centrifugal separator 6... Sludge dryer 7... Conduit 8... ...Sludge dryer 9 ... Conduit 10 ... Heat exchanger 11 ... Conduit 12 ... Arrow

Claims (1)

[Claims] 1. In a method for indirectly drying sludge, especially wastewater sludge, by mechanically pre-dewatering and/or pre-heating the sludge as the case may be, drying is carried out at low pressure on the sludge side. Do it with
A process as defined above, characterized in that in this case the low pressure is generated by absorbing steam by means of an injection condenser. 2. The method according to claim 1, wherein the low pressure is adjusted to a pressure range below 0.3 bar absolute. 3. The method according to claim 1 or 2, wherein the work is carried out by airtightly encapsulating the sludge chamber of the dryer. 4. A process as claimed in claim 3, in which the steam is sucked off in an injection condenser installed in barometric fashion and loaded with coarse sludge or waste water and condensed there. 5. The drying is carried out in two stages, in the first stage with low pressure on the sludge side and in the second stage with normal pressure or overpressure on the sludge side. The method described in any one of paragraphs to paragraphs 4 to 4. 6. The first working stage is heated using a heat carrier, for example a heat carrier oil, in which case this heat carrier is heated in a heat exchanger with steam coming from the second working stage. The method described in Section 5. 7. For example, trifluorotrichloroethane (C_2Cl_3F
7. The method according to any one of claims 1 to 6, using a fluorinated chlorinated hydrocarbon such as _3). 8. Process according to claim 7, characterized in that the flue gas generated by the sludge combustion section and flowing to the steam boiler and optionally to the air preheater is used to evaporate the heat transfer medium. 9. Transfer the flue gas to a heat transfer medium in a heat exchanger, in particular a ribbed tube heat exchanger, at a temperature higher than 60°C and/or 6.
9. A method as claimed in any one of claims 1 to 8, characterized by cooling to a temperature equal to 0<0>C. 10. Process according to any one of claims 1 to 9, characterized in that the heat transfer medium is evaporated in a heat exchanger at a temperature of 50 to 60°C, preferably 55 to 60°C. . 11. The saturated steam of the heat transfer medium coming from the heat exchanger, about 0
．． 5. A method as claimed in claim 4, in which the sludge dryer is heated with a vacuum of between 0.04 and 0.30 bar absolute pressure. 12. The method according to any one of claims 1 to 11, wherein the heat transfer medium is guided in a circulation system. 13. The sludge may be mechanically pre-dehydrated and/or
or mechanical sludge dryers (6, 8) installed in barometric style, for carrying out a process for indirectly drying sludge, in particular wastewater sludge, by preheating;
an injection condenser (1) to which it belongs, and at least one indirect sludge dryer with a gas-tightly encapsulated sludge chamber, in which case the gas dome of the sludge chamber is Device as described above, characterized in that it is connected to an injection condenser (1) via a conduit for sucking off steam. 14. A second indirect sludge dryer (8) is provided after the first indirect sludge dryer (6), in which case a second indirect sludge dryer (8) is provided for heating the heat carrier of the first sludge dryer. 14. Apparatus according to claim 13, characterized in that it is provided with a heat exchanger heated with steam coming from two sludge dryers.