RU2354613C1 - Precipitated sewage processing method and related device - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves drying the dehydrated precipitations, air-free pyrolysis with removing inorganic components of the slag precipitation and burning the produced combustible gas to generate heat in the given process. The dehydrated precipitated sewage is at first transformed into the layer 0.2-5 mm thick to be dried then while been placed on the heated surface at temperature 100-400°C. Thereafter the dried precipitation are pyrolised on the heated surface at temperature 600-800°C. Said device contains a bunker, a precipitation feed system provided at the outlet with a tool with a process slot to push the precipitation out as a thin-walled layer, a drying chamber and a pyrolysis chamber with inclined heated planes to perform drying and pyrolysis of the precipitation formed as a thin-walled layer. Said device is equipped with a combustible gas recovery system, a discharge gas and vapour disposal system; on the outlet of the pyrolysis chamber there is a slag disposal lock.

EFFECT: development of non-waste environment-friendly technology of precipitated sewage processing.

6 cl, 1 dwg, 3 ex

Description

The invention relates to methods for the disposal and processing of wet low-calorie materials of organic origin, in particular dehydrated sludge from municipal and industrial wastewater, by pyrolysis of the organic part of the sludge and the use of the resulting combustible gas for the entire process.

The problem of disposal of sewage sludge (WWS) for large cities is becoming a formidable task, because their processing to obtain valuable marketable products, such as wax, phenol, tar, etc., is not economically profitable, and their burial requires large areas that violate the environment and require additional labor and money. Therefore, numerous attempts are made to process the WWS in such a way that the process becomes waste-free.

A known method of processing dehydrated sewage sludge (RF patent No. 2211192), in which dehydrated WWS from municipal and industrial wastewater is mixed with coal, crushed and dried with hot air at the same time with the formation of solid pulverized fuel, which is burned in the furnace of an industrial boiler. The ratio of components in the mixture is as follows: dehydrated sludge 1-5%; coal - 95-99%.

The disadvantages of this method is the small proportion of WWS in the combustible mixture (1-5%), which, when processing a large amount of WWS, requires the burning of a large amount of coal. Another disadvantage is that the process of burning WWS itself is environmentally harmful, because Many harmful substances, such as cadmium, arsenic, heavy metals, etc., enter flue gases.

A known method of processing WWS to obtain liquid fuel (RF patent No. 2104970), in which the precipitate is heated to a temperature of 80-90 ° C, is mixed with heated to 100-160 ° C oil fuel oil or tar for 15-35 minutes. The ratio of WWS and oil derivatives is 75% and 25%, respectively. The resulting emulsion is used as a liquid boiler fuel. The heat of combustion of such a mixture depends on the quality of the used oil product and ranges from 5523 kJ / kg (1320 kcal / kg) to 3600 kJ / kg.

The disadvantages of this method: the combustion process releases harmful substances into the atmosphere; additionally consumed petroleum products; at the indicated ratios, the calorific value of the combustible mixture is low.

A known method of disposal of sewage sludge (RF patent No. 2198141). In this method, operating costs are reduced by optimizing the process of burning WWS in a furnace with a blast chamber through the use of automation of process control. The process includes dewatering the WWS using centrifuges and introducing a flocculant, burning the sediment in a fluidized bed in a blast furnace with the supply of hot air, natural gas and using the heat of combustion of the WWS itself.

Disadvantages: the removal into the atmosphere of harmful products of combustion of WWS.

Closest to the claimed invention, the technical solution adopted by us for the prototype is the method and device - "Obtaining valuable products from sewage sludge and other waste by the pyrolysis method" (A.Z. Evilevich, M. A. Evilevich. Utilization of sewage sludge. Stroyizdat, L.O., 1988, pp. 109-123).

The method includes drying dehydrated sludge, pyrolysis without access to air, removing the inorganic components of the sludge in the form of slag, and burning the produced combustible gas to produce heat in this process. The pyrolysis of dried WWS is carried out at a temperature of 450 ° C, and 50% of solid residues (coal, semi-coke or pyrocarbonate), 25% of liquid products (resin or primary tar), 12-15% of a mixture of gaseous products are obtained. Processing products can be further used to obtain marketable products such as wax, asphaltenes, phenols, tar, etc.

The disadvantages of this method are:

- the process of low-temperature pyrolysis at 450 ° C, in which only 12-15% of the dried precipitate is converted into gas, and the remaining components of the pyrolysis results require further processing to obtain the final commercial product, which increases their cost, and they do not withstand competition in cost with similar products obtained by other less complex methods;

- a small amount of combustible gas produced during low-temperature pyrolysis does not provide heat for the entire process, therefore additional types of fuel are consumed.

The tasks to which this invention is directed are to create an environmentally friendly processing method in which WWS are a source of energy for the entire process, which reduces emissions of harmful substances into the atmosphere, while increasing efficiency by approaching waste-free sewage sludge processing.

The technical result is achieved by the fact that in the method of processing sewage sludge, including drying of dehydrated sludge, pyrolysis without air access with the removal of inorganic components of the sludge in the form of slag and burning the produced combustible gas to produce heat in this process, the dehydrated sewage sludge is first converted into a thin-walled a layer that is dried by placing it on a heated surface, after which the dried precipitate is subjected to pyrolysis on a heated surface. The transformation of the precipitate into a thin-walled layer is carried out by extrusion through technological holes, for example in the form of a strip or "noodle" (round or flat) with a wall thickness of 0.2-5 mm. The surface in the drying chamber is heated to 100-400 ° C, the surface in the pyrolysis chamber is heated to a temperature of 600-800 ° C. A thin-walled sediment layer is moved along heated surfaces in the drying chamber and the pyrolysis chamber under the action of gravity due to their inclination to the horizontal plane.

The drying and pyrolysis process involves heating the processed material (precipitate) to the indicated temperatures. For the completeness of the process, it is necessary to warm up the entire substance, while the thermal conductivity of the substance greatly affects the heating process. For dehydrated sludge with a moisture content of 60-80%, the thermal conductivity is 0.48 W / m · deg, and for the dried sludge of 0.05 W / m · deg (Turovsky I.S. Technology of equipment for biothermal treatment of sewage sludge. M ., TsBNTI Minvodkhoz, 1988). Thus, in the heat treatment of precipitates in large masses, the drying and pyrolysis process slows down significantly when an initial dry layer with low thermal conductivity occurs. So, in the experiment, the results were obtained: a ball of sludge material with a diameter of 5 mm in a medium heated to 400 ° C, dries for 5 minutes, a film of the same material of the same mass with a thickness of 0.3-0.5 mm at the same temperature dries 10 seconds. Therefore, the first stage of the proposed method consists in converting the initial mass of sediment into a thin-walled layer by extrusion through technological holes, for example in the form of noodles or strip, with a wall thickness (diameter) of 0.2-5 mm.

The choice of the thickness of the extruded material 0.2 mm due to the fact that the material contains particles with a diameter of 0.2 in an amount up to 92% of the total mass. The choice of a thickness of 5 mm is experimentally justified: at higher thicknesses, the advantages in the drying speed of thin layers of material are lost.

The thin-walled layer (film) of the material is dried on a plane heated to 100-400 ° C. The choice of temperatures is determined by the following factors: the lower limit is the boiling point of water, the upper limit (400 °) determines the beginning of the low-temperature pyrolysis process. Intermediate temperatures must be selected on a specific installation, taking into account heat loss and a given process speed.

The choice of temperature range in the pyrolysis chamber is determined by the gasification temperature of organic substances depending on the properties of a particular precipitate, (600 ° С-800 ° С); a further increase in temperature above 800 ° C leads to additional losses of energy expended.

The proposed technology turns into combustible gas almost all the organic components of the sludge, which allows the entire process from drying to pyrolysis due to the resulting gas. The resulting gas has higher values of calorific value than when burning directly dry sediment: the calorific value of pyrolysis gas is 23430 kJ / kg (5600 kcal / kg), while when burning dry sediment the calorific value is 16736 kJ / kg (4000 kcal / kg). The amount of gas obtained and its calorific value allows the entire process (drying and pyrolysis) to be carried out at the expense of the energy contained in the WWS, which gives significant savings in natural fuel.

Closest to the invention, the technical solution for the totality of the essential features is the device that we selected for the prototype, containing a hopper (collection) of source material, a material supply system, a drying chamber with a furnace, a pyrolysis chamber with a furnace. From the pyrolysis chamber, the generated combustible gas is supplied to the furnace of the drying chamber. The device has a system for removing exhaust gases and steam (ibid., Pp. 119-121, Fig. 32).

A disadvantage of the known WWS processing device is rotary drying and pyrolysis chambers, which determines the complexity of the design of these chambers due to the mechanisms of pushing the processed sludge. In addition, the heated sludge is heated by blowing hot air from the side of the free surface, which leads to the adhesion of the sludge to the surface on which it is located. This complicates the progress of the precipitate through the drying and pyrolysis chambers. Due to low-temperature pyrolysis, the produced combustible gas is only enough to use it as an insignificant additive to the fuel in the drying chamber.

The WWS processing device that implements the proposed method is devoid of these disadvantages. The movement of the processed material does not require additional mechanisms, because it occurs under the action of gravity when it glides along inclined surfaces. The combustible gas produced during pyrolysis enters the furnaces of the drying chamber and the pyrolysis chamber, fully ensuring their operation.

The technical result is achieved due to the fact that the device for the treatment of sewage sludge contains a hopper, a sludge supply system, a drying chamber and a pyrolysis chamber with corresponding furnaces, a system for removing the produced combustible gas and a system for removing exhaust gases and steam. In addition, the outlet supply system has a device with a technological slot for squeezing out the sediment in the form of a thin-walled layer into the drying chamber on an inclined surface heated from the furnace of the drying chamber. The drying chamber is connected to the pyrolysis chamber through a gateway, from where the precipitate falls on the inclined surface of the pyrolysis chamber, heated from the furnace of this chamber. The pyrolysis chamber has a system for removing the produced combustible gas connected through gas purification and distribution devices to the furnaces of the drying and pyrolysis chambers, and a gateway for removing slag is installed at the outlet of the pyrolysis chamber. The inclined surfaces of the drying chamber and the pyrolysis chamber are inclined to the horizontal plane at angles of 40 ° ± 10 ° and 35 ° ± 10 °, respectively.

To accelerate the processes in the device, the initial precipitate is converted into thin-walled layers in the form of noodles (round or flat) or in the form of a strip using a device with a technological gap of the appropriate profile for forcing the material.

The movement of material in the drying chamber and the pyrolysis chamber is carried out on inclined surfaces under the action of gravity without the use of additional mechanisms. This becomes possible due to the fact that the sediment is heated through the surface on which it is located, while the friction force of the sediment on the surface is greatly reduced due to the formation of steam and gas between the sediment and the heating surface. The optimal angles of inclination of the planes are selected experimentally.

The pyrolysis chamber is equipped with lock chambers at the inlet and outlet for carrying out the pyrolysis process without air access.

The drawing shows a diagram of the proposed device.

A device for treating sewage sludge contains a hopper 1, a sludge supply system 2, a drying chamber 3 and a pyrolysis chamber 4 with corresponding furnaces 5 and 6, a system for removing 7 produced combustible gas, and an exhaust gas and steam removal system 8. The sludge supply system 2 at the outlet has a device 9 with a technological slot for squeezing out the sludge in the form of a thin-walled layer 10 into the drying chamber 3 onto an inclined surface 11 heated from the furnace 5 of the drying chamber 3. The drying chamber 3 is connected to the pyrolysis chamber 4 through a lock 12, from where the precipitate falls on the inclined surface 13 of the pyrolysis chamber 4, heated from the furnace 6 of this chamber. The pyrolysis chamber 4 has a system for removing the produced combustible gas 7, which is connected through purification devices 14 and gas distribution 15 to the furnaces of the drying chambers 5 and pyrolysis 6. At the outlet of the pyrolysis chamber 4, a gateway 16 is installed for removing slag. The inclined surfaces 11 and 13 of the drying chamber 3 and the pyrolysis chamber 4 are inclined to the horizontal plane at angles α = 40 ° ± 10 ° and β = 35 ° ± 10 °.

In addition, the drawing shows the valves 17, 18, 19 of the gas distribution system 15; adjustable valve 20 to maintain the required excess pressure of the combustible gas in the system; torch 21 of combustion of excess combustible gases; exhaust fan 22; a drive shaft 23 of the mechanisms of the lock chambers 12 and 16; kinematic connection 24 between the lock chambers; electric drive 25 kinematic connection 24.

The processing device WWS works as follows.

The dehydrated WWS enter the hopper 1, from where they are supplied with a feed system 2, for example, with a gear or screw pump, are forced through the technological hole of the device 9 to obtain a thin-walled layer 10, for example, in the form of “noodles” or strips 0.2–5 mm thick and with a width that ensures required installation performance. The precipitate in the form of a formed thin-walled strip 10 enters the drying chamber 3 on an inclined surface 11, heated by means of a furnace 5 to temperatures of 100-400 ° C. Between the sediment layer 10 and the heated surface 11 there is a layer of steam due to the evaporation of moisture contained in the precipitation. The vapor eliminates the adhesion of the sediment layer 10 to the surface 11, the slope of which to the horizon is an angle α = 40 ± 10 °, chosen experimentally. The presence of a vapor layer between the sediment layer 10 and the heated surface 11 reduces friction, and the layer 10 slides down the surface 11 due to gravity without additional pushing forces (in the drawing, the sediment layer 10 is shown by a thick dashed line). During the passage of the drying chamber 3, the precipitate dries to a moisture content of 10-20%, with an initial humidity of 70-80%.

From the drying chamber, the sediment layer 10 enters the lock chamber 12 at the entrance to the pyrolysis chamber 4. Precipitation can be supplied to the lock chamber 12 in doses that are discharged through the lock 12 into the pyrolysis chamber 4, thus preventing air oxygen from entering therein.

In the pyrolysis chamber 4, the sediment enters the inclined surface 13, heated by the furnace 6 to temperatures of 600-800 ° C. The inclination of the plane 13 to the horizon, determined experimentally, makes an angle β = 35 ± 10 °, at which the sediment moves steadily under the influence of gravity on the surface 13 to the lock 16, which serves to remove slag from the pyrolysis chamber and prevents air from entering it .

The mechanism of movement along the inclined surface 13 of the sediment under the action of gravity is due to the occurrence of a layer of combustible gas between the sediment layer and the heated surface 13, which reduces friction. During the passage of the pyrolysis chamber 4, the organic component of the precipitate at temperatures of 600 ° C-800 ° C turns into combustible gas, which enters the system of removal of combustible gas 7, then passes the purification system 14 and then to the gas distribution system 15.

Through valves 17 and 18, the purified combustible gas enters the furnace 5 of the drying chamber 4 and into the furnace 6 of the pyrolysis chamber 4. The valve 19 serves to start the operation of the entire installation in the initial period when there is no accumulated combustible gas. Through this valve, pre-stored flammable gas or natural (balloon) gas enters the system to heat planes 11 and 13. After flammable gas begins to be emitted in the pyrolysis chamber 4, valve 19 closes. If necessary, through the valve 19, the gas distribution system 15 can, during the operation of the device, receive additional natural gas if consignment of WWS with a low hydrocarbon content is sent.

The automatic valve 20 maintains a pressure in the system (80-300 mm water column) suitable for use in standard gas burners installed in the furnaces 5 and 6 of the drying chamber 3 and the pyrolysis chamber 4. Excessive combustible gas after valve 20 enters the open torch 21.

The gateways 12 and 16 of the pyrolysis chamber 4 are synchronized by an electric motor 24 through a kinematic connection 23.

The exhaust gases and steam from the drying chamber 3 and the pyrolysis chamber 4 enter the removal system 8 (exhaust system) with a fan 22, from which they are discharged into the atmosphere.

From the pyrolysis chamber 4 at the outlet through the gateway 16, slag is removed into the slag collector 26.

The rationale for the implementation of the method.

Example 1

Obtaining a thin-walled layer of WWS. The process of extruding material through a flat die was studied. The characteristics of the formation of a thin-walled layer of the starting material are experimentally obtained. The following pressures were obtained for extruding the WWS material through flat dies: for a film with a thickness of 0.2 mm — 3.2 kg / cm ² , when forcing through a 1 mm slot — 2.7 kg / cm ² , through a 2 mm slot — 2.1 kg / cm ² . At the indicated sizes and pressures, the material is extruded in an even layer.

Example 2

Drying thin sheets of material. The material in the form of a sheet with a given thickness of 1 mm at a moisture content of 75-82% was placed on a flat surface heated to a given temperature, and the following moisture removal rates were obtained:

Surface temperature Drying speed 200 ° C 7.8 mg / s 400 ° C 15 mg / s

Example 3

Spontaneous movement of material on a heated surface. Material in the form of a layer with a thickness of 1-2 mm was laid on a surface heated to 200 ° C, 400 ° C and 800 ° C, the angle of inclination of the surface to the horizon until stable rolling under the influence of gravity changed. The following results were obtained: for temperatures up to 400 ° C - angles of 35 ± 10 ° are necessary, and for at a temperature of 800 ° C - 30 ± 10 °. The angle of inclination depends on the quality of the heated surface and the moisture content of the material. In the experiments, no adherence of the material to the heated surface was observed anywhere.

Example 4. When the capacity of the WWS utilization plant is 250 kg per hour (69.4 g / s), the moisture content of the dehydrated sludge is 75%, the dry matter content is 25%, and the slag content is 40%.

Thermal data of the WWS: heat capacity of the raw material 2.97 J / g · deg, heat capacity of the dry material 1.59 J / g · deg, thermal conductivity wet / dry 0.48 / 005 W / m · deg.

4.1. Heat Q _sushi drying 69.4 g / s SALT with the heating and evaporation requires heat Q _LOAD 138.2 J / s.

4.2. The heat required for the pyrolysis of the mass of dried 17.35 g / s sludge with an organic content of 60% with heating from 150 ° C to 800 ° C (Δt = 650 ° C) is Q _pir = 17.9 J / s.

4.3. The amount of combustible gas obtained from the dry sludge (25% of the initial mass) and 60% of the organic matter content in it will be m _{g / g} = 10.41 g / s.

4.4. The amount of heat obtained by burning combustible gas in burners, with its calorific value of 5600 kcal / kg or 23.430 kJ / kg:

Q _{g / g} = 23.43 × 10.41 = 243.9 kJ / s.

4.5. The total waste of heat on the drying and pyrolysis process with an efficiency of thermal processes of 0.7 will be:

Q _shutter = (Q _sushi + Q _pir ) /0.7 = 156.1 / 0.7 = 223 kJ / s.

4.6. The energy balance is positive: produced 244 J / s, spent 223 J / s, a positive balance of 21 J / s or 75.6 kW per hour of operation, which amounts to 1814 kWh per day.

The experiment correlates well with the above calculation and shows that the resulting combustible gas is enough to carry out the whole process.

Thus, the proposed method and device fully cover the costs of the process, which corresponds to the task. The technology provides saving of natural fuel, reducing harmful emissions and improving the ecology of the process, as the heat for the process is obtained by burning combustible gas obtained by pyrolysis from organic components of WWS and having a sufficiently high calorific value of 5600 kcal / kg. Harmful substances remain in the slag. When pyrolysis, toxic substances are destroyed, there is an effective disposal of waste; the amount of slag by volume is approximately 1/10 of the recycle WWS. Slag can be used as a mineral filler in construction, in road surfaces, etc. Thus, the invention allows to create a waste-free processing of WWS.

Claims (6)

1. A method of processing sewage sludge, including drying of dehydrated sludge, airless pyrolysis with the removal of inorganic components of the sludge in the form of slag and burning the produced combustible gas to produce heat in this process, characterized in that the dehydrated sewage sludge is first converted into a thin-walled layer which is dried by placing it on a heated surface, after which the dried precipitate is subjected to pyrolysis on a heated surface. 2. The method according to claim 1, characterized in that a thin-walled layer of sediment is formed in the form of a strip or "noodle" (round or flat) with a wall thickness of 0.2-5 mm. 3. The method according to claim 1, characterized in that the surface in the drying chamber is heated to 100-400 ° C, the surface in the pyrolysis chamber is heated to a temperature of 600-800 ° C. 4. The method according to claim 1, characterized in that the thin-walled layer of sediment is moved over heated surfaces during drying and during pyrolysis under the action of gravity due to the inclination of the surfaces to a horizontal plane. 5. A device for processing sewage sludge containing a hopper, a sludge supply system, a drying chamber and a pyrolysis chamber with corresponding furnaces, a system for removing combustible gas produced and an exhaust gas and steam removal system, characterized in that the outlet sludge supply system has a device with technological gap for squeezing out the precipitate in the form of a thin-walled layer into the drying chamber on an inclined surface heated from the furnace of the drying chamber, the drying chamber is connected to the pyrolysis chamber through a gateway onnuyu pyrolysis chamber surface heated by the furnace of the chamber, the pyrolysis chamber communicates with the system produced by the fuel gas outlet connected via a gas purification and distribution devices furnaces drying and pyrolysis chambers, and the outlet of the pyrolysis chamber is mounted gateway for removing slag. 6. The device according to claim 5, characterized in that the inclined surfaces of the drying chamber and the pyrolysis chamber are installed at angles to the horizontal plane of 40 ± 10 ° and 35 ± 10 °, respectively.