RU2819544C1 - Catalytic waste heat boiler for incineration of sewage sludge of enterprises and method of their incineration - Google Patents

Abstract

FIELD: processing and recycling of wastes.

SUBSTANCE: group of inventions is intended for processing of wet sludge from industrial, municipal and other enterprises and can be used to reduce anthropogenic load on surrounding territories. Catalytic waste heat boiler for incineration of sewage sludge of enterprises is a vertical cylindrical boiler of variable diameter from stainless steel, equipped with an air supply unit in the lower part of the housing, catalyst feed branch pipe is arranged at housing top, sewage sludge and additional fuel feed branch pipes are arranged above said nozzle. Supply of sewage sludge is carried out through four nozzles of round section welded into the boiler housing in one plane, equidistant from each other and connected by pipes with two dosing devices operating in parallel. When burning waste water sludge in fluidized bed mode, the above-described waste heat boiler is used. Process is carried out at temperature of 650–800 °C using a mixture of an inert material in amount of 50–80 vol.% and a catalyst for deep oxidation of organic substances and CO in amount of 20–50 vol.%. Catalyst for deep oxidation of organic substances and CO is a mixture of transition metal oxides as an active component and oxides of alkali and/or alkali-earth metals as a promoter. Carrier is represented by materials consisting of oxides of aluminum, silicon or mixtures thereof with a developed specific surface area.

EFFECT: higher efficiency, manifested in increase in uniformity of supply of wet sludge waste water to waste heat boiler, in reduction of specific consumption of catalyst per ton of burnt sludge during combustion of sewage sludge due to more uniform distribution of velocities over boiler cross-section, reduction of heat load on material of external wall and welded seams of housing, increase of service life of steel reactor housing.

4 cl, 3 dwg

Description

The invention relates to devices and methods for processing wet sludge from wastewater from industrial, municipal and other enterprises, and can be used to reduce the anthropogenic load on surrounding areas.

A known catalytic reactor for processing sewage sludge and a method for processing it according to patent RU 2536510 C2 - [1], consisting of a housing expanded in the upper part, equipped with a sewage sludge supply pipe at the level of the connection of the lower and upper parts of the housing, pipes for unloading inert material and air and fuel supply in the lower part of the housing, pipes for removing flue gases and loading inert material in the upper part of the housing, a gas distribution grid located between the air and fuel supply pipes, on which particles of dispersed inert material are located, organizing nozzles and heat exchange surfaces sequentially placed above the grill . In this case, the organizing nozzle is made of materials containing an oxidation catalyst. The presented method for processing sewage sludge includes mechanical dewatering of the sludge, heat treatment of the concentrate in a fluidized layer of dispersed particles organized by a stationary nozzle at a temperature of 700-750°C in excess air above or equal to α≥1.2, separation of solid products from flue gases, cooling solid processing products, storage or disposal of solid products.

The disadvantages of the catalytic reactor and methods for the catalytic processing of sewage sludge [1] are: the complexity of manufacturing a stationary catalytic nozzle, uneven supply and distribution of sludge sludge in the reactor due to the presence of only one supply pipe, which leads to an unstable boiling regime of bed particles in the reactor and the possibility of overload reactor with processed material, which, in turn, leads to the need to stop the system and clean the reactor. The disadvantages of the presented first method include the use of significant quantities of auxiliary reagents, including solutions of inorganic acids, for washing and purifying the product of thermal processing of sewage sludge. This approach leads to the need for increased control over the safety of wastewater generated in the process. The disadvantages of the presented second method include the use of a stationary catalytic nozzle, which leads to uneven occurrence of the reactions of deep oxidation of organic substances and CO released during the combustion of sewage sludge throughout the volume of the fluidized bed. This leads to the possibility of exceeding the content of harmful substances in the flue gases.

Also known is a catalytic reactor for processing sewage sludge and a method for processing it according to patent RU 2456248 C1 - [2]. The combustion process is carried out in a fluidized bed of a mixture of catalyst and inert material organized by a stationary nozzle with a catalyst content of 20-90% at a temperature of 700-750 C with excess air α≥1.2. The disadvantages of the reactor design [2] in this method in the case of combustion are: the introduction of sediment at only one point, which leads to an uneven distribution of the gas flow across the cross section of the apparatus when feeding wet sediment, which will lead to the mechanical ejection of particles from the layer; the location of the heat exchanger in the upper part of the layer complicates the process of putting the reactor into operation; in the case of highly humid precipitation with a low calorific value, additional heat removal from the layer due to the emission of particles onto the heat exchange surfaces will lead to a decrease in the temperature in the layer, as a result of which it is necessary to introduce a larger amount of additional fuel ; deformation of the welds of the reactor vessel.

The prototype that is closest in technical essence to the stated technical solutions is a catalytic reactor for recycling sewage sludge from municipal wastewater treatment plants and a method of recycling described in patent RU 2752476 C1 - [3]. The reactor consists of a vertical body, in the upper part of which there is a catalyst supply pipe, in the lower part there are two pipes for supplying sludge, a screw supply of coal, and removal of the catalyst from the reactor. Inside the reactor, in the upper part, there is a bumper in the shape of a hollow truncated cone; in the middle part there is an organizing nozzle, while in the lower part of the body there is an air distribution device, and at the base of the reactor body there is an unloading auger for unloading non-combustible components of sewage sludge.

The disadvantages of a catalytic reactor for recycling sewage sludge from municipal treatment plants and methods of recycling are: uneven supply and distribution of sludge in the reactor, increased consumption of catalyst and carrier due to abrasion and the emission of particles due to uneven velocity distribution across the cross section of the reactor as a result of feeding sludge through one pipe , deformation of the welds of the reactor vessel, increased abrasion of particles during the process of unloading the reactor with a screw conveyor, the formation of large gas bubbles in the combustion zone due to the lack of an organizing lattice.

Among the disadvantages of analogues [1], [2] and prototype [3], the task of the claimed invention is to increase the efficiency of the process of burning sewage sludge from industrial and municipal enterprises under fluidized bed conditions.

The essence of the claimed device - a catalytic waste heat boiler for burning sewage sludge from enterprises (industrial, municipal, etc.) is a vertical cylindrical boiler of variable diameter made of stainless steel, equipped with an air supply unit in the lower part of the housing, a catalyst supply pipe in the upper part of the housing, pipes for supplying sewage sludge and additional fuel, above which an organizing nozzle is located. In this case, the supply of sludge sewage sludge is carried out through four round pipes welded into the boiler body in one plane (horizontal), equidistant from each other and connected by pipes with two dosing devices operating in parallel (which ensures uniform supply of wet sludge sewage sludge into recovery boiler, as well as a reduction in the specific consumption of catalyst per ton of burned sludge in the process of burning sewage sludge due to a more uniform distribution of velocities across the cross section of the boiler). The pipes for introducing sludge into the boiler can be equipped with internal sludge mass dividers, which are two mutually perpendicular stainless steel plates located along the sludge flow. The inner wall of the boiler can be lined with monolithic heat-resistant low-cement concrete with a heat-insulating layer (which reduces the thermal load on the material of the outer wall and the welds of the body, as well as increases the service life of the steel body of the catalytic waste heat boiler.).

The essence of the claimed method of operation of the above device - a method of burning sewage sludge in a fluidized bed mode in a recovery boiler, at a temperature of 650-800 ° C, is that the process is carried out using a mixture of inert material in an amount of 50 vol.% and a catalyst deep oxidation of organic substances and CO in an amount of 20-50 vol.% (which reduces the consumption of expensive catalyst). In this case, the catalyst for the deep oxidation of organic substances and CO is a mixture of transition metal oxides as an active component and alkali and/or alkaline earth metal oxides as a promoter; materials consisting of aluminum oxides, silicon or their mixtures with a developed specific surface act as a carrier .

The technical result of the presented invention (claimed technical solutions - device and method of its operation) is an increase in efficiency, manifested in:

1. Increasing the uniformity of supply of wet sludge from wastewater to the recovery boiler.

2. Reducing the specific catalyst consumption per ton of burned sludge in the process of burning sewage sludge due to a more uniform distribution of velocities across the cross section of the boiler.

3. Reducing the thermal load on the outer wall material and body welds.

4. Increasing the service life of the steel reactor vessel.

The essence of technical solutions is further revealed by graphic materials, where in Fig. 1 shows a longitudinal vertical section of a catalytic waste heat boiler, and FIG. 2 and fig. 3, respectively, its transverse (horizontal) sections A-A and B-B.

The figures indicate: I - first catalytic combustion zone, II - second catalytic combustion zone, III - separation zone, 1 - vertical steel body of the catalytic waste heat boiler, 2.1 and 2.2 - additional fuel supply pipes, 3 - gas distribution cap grid, 4.1, 4.2, 4.3 and 4.4 - sludge supply pipes; 5 - flue gas exhaust pipe, 6 - inert material and catalyst loading pipe, 7 - package of volumetric organizing nozzle of the first combustion zone (I), 8 - package of volumetric organizing nozzle of the second combustion zone (II).

The above technical result is solved by the design of a catalytic waste heat boiler designed for burning wastewater sludge from industrial and municipal enterprises under fluidized bed conditions. The catalytic waste heat boiler (hereinafter referred to as the boiler) consists of a stainless steel body (1), the inner wall of which is lined with monolithic heat-resistant low-cement concrete with a heat-insulating layer (not shown in the figures). The housing (1) is a vertical structure with an extension at the top. The upper part of the boiler is equipped with pipes (6) for supplying catalyst and inert material, as well as a pipe (5) for removing flue gases. At the level of the connection of the lower and upper expanded part of the reactor body (1) there are pipes (4.1, 4.2, 4.3 and 4.4) for supplying sewage sludge of round cross-section, welded into the boiler body (1) in the same horizontal plane and equidistant from each other, connected pipes with two dosing devices operating in parallel. The nozzles located diametrically opposite (4.1, 4.2, 4.3 and 4.4) are connected to one pump (not shown in the figures). In the lower part of the boiler body (1) there are pipes (2.1 and 2.2) for supplying additional fuel. Inside the housing (1), below the nozzles (2.1 and 2.2) for supplying additional fuel, there is a gas distribution cap grille (3). Above the nozzles (2.1 and 2.2) for supplying additional fuel, as well as above the nozzles (4.1, 4.2, 4.3 and 4.4) for supplying sludge, organizing nozzles (7 and 8) are placed, respectively. Also, the technical result is achieved by the design of the boiler, which consists of a stainless steel body (1), the inner wall of which is lined with monolithic heat-resistant low-cement concrete with a heat-insulating layer (not shown in the figures).

The technical result is also achieved by the claimed method of burning sewage sludge from industrial and municipal enterprises under fluidized bed conditions. The method involves burning sewage sludge at 650-800°C in a fluidized bed of a mixture of inert material (in an amount of 50-80 vol.%) and a catalyst for the deep oxidation of organic substances and CO (in an amount of 20-50 vol.%). In this case, the catalyst for the deep oxidation of organic substances and CO is a mixture of transition metal oxides as an active component and alkali and/or alkaline earth metal oxides as a promoter. The carrier is an oxide material with a developed specific surface area, consisting of aluminum oxides, silicon oxides or mixtures thereof.

The inert material is a material of oxide nature, more than 95 wt. % consisting of oxides of aluminum, silicon, magnesium, iron or mixtures thereof.

The combustion of sewage sludge is carried out by feeding the material into a recovery boiler heated to 650-800°C and containing a mixture of inert material and a catalyst for the deep oxidation of organic substances and CO or only the catalyst. At this time, the air necessary for the oxidation and liquefaction of particles of inert material and catalyst is also supplied to the boiler.

As a measure of catalyst abrasion, the amount of catalyst mass loss in the target fraction (>1.4 mm) when abraded for 90 minutes in a steel drum according to ASTM D 4058 was chosen.

The catalytic waste heat boiler is a vertical housing (1), consisting of three parts - the first catalytic combustion zone (I), the second catalytic combustion zone (II) and the separation zone (III). The cross-sectional areas of the first catalytic combustion zone (I) and separation zone (III) are selected in such a way that the linear velocities of particles in them do not exceed 80% of the entrainment onset speed at 750°C. The total height of the combustion zones (I) and (II) is at least 1 m. The total height of the waste heat boiler is at least 3 times the diameter of the separation zone (III). In the first combustion zone (I), the boiler body is equipped with pipes (2.1 and 2.2) for supplying additional fuel and a gas distribution cap grille (3). In the second combustion zone (II), the housing (1) is equipped with pipes (4.1, 4.2, 4.3 and 4.4) for supplying sludge. In the upper part of the separation zone, the boiler body is equipped with pipes: (5) - flue gas removal and (6) - loading of inert material and catalyst. Above the gas distribution cap grid (3) inside the first combustion zone (I) and above the nozzles (4.1, 4.2, 4.3 and 4.4) for supplying sludge in the second combustion zone (II), packages of volumetric organizing nozzles (7) and (8) with the size of the holes is 10-100 diameters of particles of inert material and the proportion of free volume in the package of nozzles is 85-95%. The nozzles (7) and (8) are made in the form of fixed blocks, the elements of which are gratings.

A catalytic waste heat boiler works as follows. Inert material or catalyst is loaded into the boiler through the loading pipe (6). The amount of inert material or catalyst is 30-50% of the total volume of the layer material. The layer of particles of inert material or catalyst is heated to a temperature of 300-500°C, for example, due to heated air supplied through the cap grid (3) to fluidize the layer. Then additional fuel is introduced into the layer through pipes (2.1 and 2.2). The temperature of the layer is adjusted to 650-700°C due to the heat of combustion of the fuel. Upon reaching the required temperature, additional loading of inert material and/or catalyst into the boiler is carried out through the pipe (6). The total amount of inert material and/or catalyst loaded into the boiler must correspond to the height of the fluidized bed at the operating fluidization speed in the upper part of the body so that the upper organizing nozzle (8) is completely immersed in the bed. After loading the material, the layer is heated to 700-750°C and the supply of sludge begins through the pipes (4.1, 4.2, 4.3 and 4.4). The supply of additional fuel through the pipes (2.1 and 2.2) is reduced or stopped depending on the operating temperature of sludge combustion.

The method is carried out as follows. Sludge sludge after mechanical dehydration with a humidity of 60-80% is fed into the second combustion zone (II) of a catalytic waste heat boiler with an organized fluidized bed of inert material and a catalyst or only a catalyst. The fluidized layer is created by air, which is supplied under the gas distribution cap grid. When sludge sludge enters and passes through a fluidized layer of catalyst particles and inert material or just the catalyst, water evaporates and heats up to the operating temperature of the boiler, heating the dry sludge particles with the release of volatile substances and their oxidation in the presence of catalyst particles. The required temperature of the layer is maintained due to the calorific value of the sludge. When the temperature in the boiler decreases due to changes in the characteristics of the sediment, additional fuel is introduced into the bed. After the layer, the flue gases are sent for cleaning and discharge through the pipe (5).

Examples of implementation of a method for burning sewage sludge in a fluidized bed mode in a waste heat boiler.

Example 1 (prototype).

Only the industrial deep oxidation catalyst Mg-Cu-Cr-Al-O with an average particle size of 2-3 mm is loaded into the recovery boiler as a fluidized bed material. The catalyst is heated to 700-750°C, after which sewage sludge is fed into the boiler. As the process progresses, the catalyst wears out, leading to a decrease in the pressure drop between the lower and upper parts of the boiler, which indicates the need to additionally load the catalyst into the recovery boiler.

The weight loss of the catalyst in the target fraction (>1.4 mm) during attrition, carried out according to ASTM D 4058, is about 5 wt. %, which corresponds to 50 kg of catalyst per 1 ton of layer material.

Example 2.

Similar to example 1, only a mixture of catalyst and inert material is loaded into the recovery boiler in a ratio of 1:1 by weight.

The weight loss of the catalyst in the target fraction (>1.4 mm) during attrition, carried out according to ASTM D 4058, is about 7 wt. %, which corresponds to 35 kg of catalyst per 1 ton of layer material.

Example 3.

Similar to example 1, only a mixture of catalyst and inert material is loaded into the recovery boiler in a ratio of 1:4 by weight.

The weight loss of the catalyst in the target fraction (>1.4 mm) during attrition, carried out according to ASTM D 4058, is about 10 wt. %, which corresponds to 20 kg of catalyst per 1 ton of layer material.

Literature

1. Patent for invention of the Russian Federation: RU 2536510 C2 dated December 27, 2014, IPC C02F 11/06, F23C 10/01, “Catalytic reactor for processing sewage sludge and a method for their processing (Options)” patent holder: Federal State Budgetary Institution of Science Institute catalysis named after G.K. Boreskov of the Siberian Branch of the Russian Academy of Sciences (RU).

2. Patent for invention of the Russian Federation: RU 2456248 C1 from 07/20/20212, IPC C02F 11/06, F23C 10/01, F23C 13/04, D21C 11/04, C02F 103/28, “Catalytic reactor for processing sewage sludge and method of their processing (Options)", patent holder: Institution of the Russian Academy of Sciences Institute of Catalysis named after. G.K. Boreskov of the Siberian Branch of the Russian Academy of Sciences (RU).

3. Patent for invention of the Russian Federation: RU 2752476 C1 dated 07/28/2021, IPC C02F 11/06, C02F 11/18, F23C 10/01, F23C 13/08, “Catalytic reactor for recycling sewage sludge from municipal treatment facilities and method of implementation recycling", patent holder: Limited Liability Company "RVK. Catalysis" (LLC "RVK. Catalysis") (RU) - prototype.

Claims (4)

1. Catalytic recovery boiler for burning sewage sludge from enterprises, which is a vertical cylindrical boiler of variable diameter made of stainless steel, equipped with an air supply unit in the lower part of the body, a catalyst supply pipe in the upper part of the body, pipes for supplying sewage sludge and additional fuel , above which there is an organizing nozzle, characterized in that the supply of sewage sludge is carried out through four round pipes, welded into the boiler body in the same plane, equidistant from each other and connected by pipes with two dosing devices operating in parallel. 2. Catalytic waste heat boiler according to claim 1, characterized in that the sludge input pipes into the boiler are equipped with internal sludge mass dividers, which are two mutually perpendicular stainless steel plates located along the sludge flow. 3. Catalytic waste heat boiler according to claim 1, characterized in that the inner wall of the boiler is lined with monolithic heat-resistant low-cement concrete with a heat-insulating layer. 4. A method for burning sewage sludge in a fluidized bed mode in a waste heat boiler, which is a vertical cylindrical boiler of variable diameter made of stainless steel, equipped with an air supply unit in the lower part of the body, a catalyst supply pipe in the upper part of the body, and pipes for supplying sludge sewage sludge and additional fuel, above which there is an organizing nozzle, configured to supply sewage sludge through four round pipes welded into the boiler body in one plane, equidistant from each other and connected by pipes with two dosing devices operating in parallel, characterized by that the process is carried out at a temperature of 650-800°C, using a mixture of inert material in an amount of 50-80 vol.% and a catalyst for the deep oxidation of organic substances and CO in an amount of 20-50 vol.%, while the catalyst for the deep oxidation of organic substances and CO is a mixture of transition metal oxides as an active component and alkali and/or alkaline earth metal oxides as a promoter; materials consisting of aluminum oxides, silicon or their mixtures with a developed specific surface area act as a carrier.

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