CH720670A2 - Device for thermal carbonization of municipal sludge - Google Patents

Abstract

The invention relates to a device for the thermal carbonation of municipal sludge, comprising an inlet (1) for the dosing of dried municipal sludge and an alkaline carbonation agent, a hopper (2) with extruder and degassing, and a dosing screw (4) with motor (16) which opens into the area of the thermal carbonator (3) in order to carbonize the introduced dried sludge. The thermal carbonator (3) is equipped with electrical heating of the interior through its outer jacket and has a screw driven by a motor (8) which moves the carbonated mixture through the carbonator. It consists of the electrically heated first (5) and second (6) temperature zones. At the end of the first temperature zone (5), the gas phase from the carbonator is passed through a pipe into a cooled condenser (9) in order to condense part of the gas phase. At the end of the second temperature zone (6) there is an outlet device for the discharge of the resulting solid carbonated substance into a screw conveyor (11) with motor (17) and cooling by cooling water (7). At the end of the screw conveyor (11) the cooled solid carbonated substance is discharged into its container (12). The cooled condenser (9), which receives part of the gas phase from the carbonator, is connected to a mechanical-chemical-biological treatment plant (10) to separate the liquid (13) and gaseous (14) components, which are then fed into the mechanical-chemical-biological treatment plant system for further processing.

Description

[0001] This invention relates to an apparatus for thermal carbonization of municipal sludge.

State of the art

[0002] Until now, sludge from municipal sewage treatment plants was used for classic "fertilization", i.e. the land was irrigated with liquid sludge. Another method is to dewater the sludge and mix it with green biowaste and wood chips to make compost. None of these processing methods guarantees the destruction of the undesirable organic and inorganic substances contained in the sewage sludge. These substances continue to enter the soil and secondarily into the cultivated plants.

[0003] Another method for sludge destruction is the incineration of the thickened sludge. This method is very expensive in terms of energy and releases emissions into the atmosphere.

[0004] Another method is to dry municipal sludge and deposit it in municipal waste landfills. Landfilling sludge dried in this way is cheaper than landfilling liquid sludge due to the fees involved. By dewatering and drying, the producer reduces the weight of the sludge and thus the disposal costs.

representation of the invention

[0005] Due to the above facts, the task was to develop a device for thermal carbonization that offers an efficient and ecological technical solution to the problems mentioned.

[0006] The invention is solved by the features of the first patent claim.

[0007] The device according to the invention for thermal carbonization of municipal sludge with the assistance of an alkaline carbonizing agent enables the conversion of municipal sludge into an economically advantageous resource - carbonized carbon substance.

[0008] It consists of an inlet for the dosing of dried sludge and an alkaline carbonating agent, which opens into a hopper with an extruder and degassing, as well as a dosing screw with motor and a thermal carbonator. The dosing screw leads to the area of the thermal carbonator for carbonation of the incoming dried sludge mixed with the alkaline carbonating agent.

[0009] The thermal carbonator is equipped with a motor-driven screw to transport the mixture through the carbonator. The carbonator comprises two temperature zones, namely the first temperature zone I and the second temperature zone II. An electric heater is housed in the jacket of the thermal carbonator.

[0010] At the end of the first temperature zone I there is the outlet of the gas phase from the thermal carbonator, and at the end of the second temperature zone II there is the outlet for removing the resulting carbonized solid substance to the inlet into the screw with motor and cooling by cooling water. At the end of the screw there is the outlet of the cooled solid carbonized mixture into its storage tank. The thermal carbonator is connected via a gas phase pipe to a cooled condenser for condensing part of the gas phase from the thermal carbonator, and the condenser is connected to a separation unit for separating the liquid and gaseous components, which are fed from the separation unit into the mechanical-chemical-biological treatment plant system for further processing.

[0011] The device for thermal carbonization of municipal sludge has a programmable logic controller (PLC) for controlling and monitoring the technological process. The PLC system can also be used remotely, which allows continuous control without direct human supervision, with an energy consumption of about 45 kW (0.45 kW per 1 kg). The PLC system includes, in particular, measurement and control of the temperature in both zones of the carbonizing thermal reactor and in the cooling screw for the produced carbonized solid substance, including measurement and control of the cooling water for cooling the screw and the gas phase condenser.

[0012] The municipal sludge is dried to a dry matter content of 80% to 90% before entering the device and mixed at the inlet of the device with an alkaline carbonating agent in an amount of 4 to 6% by weight of the dry matter of the dried sludge. The alkaline carbonating agent consists of an alkaline mixture of 0.1% to 1.5% by weight of alkalis and the rest up to 100% by weight consists of biomass. The alkaline mixture contains alkaline hydroxides, hydroxides of alkaline earths, carbonates, bicarbonates or mixtures thereof. Biomass consists of lignocellulose and/or cellulose in the form of grains, semolina, sawdust, straw, fibers or waste paper.

[0013] The residence time in the thermal carbonizer varies depending on the dry matter content of the dried sludge and is on average 15 minutes.

[0014] The temperature of the resulting carbonized solid substance after cooling does not exceed 40 °C. In the process of thermal carbonization of municipal sludge, in addition to microplastics, antibiotics, antidepressants, contraceptives, drugs are destroyed, and bacteria and viruses contained in it are eliminated. The amount of the resulting carbonized solid substance per unit of the starting material - dried sludge - is 65% to 75% of the mass, depending on the dry matter content and other qualitative parameters of the incoming dried sludge. This value refers to elemental carbon and carbon bound to undegraded organic residues. The carbon can be used in various industries and is no longer waste, but a raw material for industry and agriculture. The carbon content (both free and bound) in the carbonized solid substance is between 35% and 55%.

[0015] The device for thermal carbonization of municipal sludge is an efficient and ecological solution for improving the environment. Municipal sludge, which has a significant impact on the environment, is converted into a carbonized solid carbon substance by removing the microplastics, antidepressants, contraceptives, drugs and eliminating bacteria and viruses. The carbon substance can serve as a starting material for other sectors of industry and agriculture. The carbonized solid carbon substance is usable in various sectors of industry and agriculture and is not waste but a raw material.

Short description of the drawings

[0016] The invention is explained in more detail with reference to the drawing. It shows: Fig. 1 the device for the thermal carbonization of municipal sludge in a schematic representation.

Examples of the implementation of the technical solution

Example 1

[0017] Municipal sludge, dried to a solids content of 85% (15% water content), is mixed with 4.5% of an alkaline carbonating agent. This consists of 1.2% NaOH, the rest up to 100% is biomass from lignocellulose. The mixture is conveyed via inlet 1 into the hopper 2 with extruder and degassing, then passed through the dosing screw 4 with motor 8 into the thermal carbonizer 3 at 550 °C. The carbonized mixture moves through the carbonizer, driven by a screw motor 16, through the temperature zone I 5 and temperature zone II 6. After the mixture has passed through the temperature zone I, the gaseous phase is passed through a pipe into the condenser 9 at the end of this zone. In the temperature zone II, a carbonized solid substance is formed by the action of heat and the alkaline carbonating agent. In the cooled condenser 9, the gaseous phase partially condenses and the liquid component 13 and the gaseous component 14 are sent to the mechanical-chemical-biological treatment plant 10. After their separation, they are returned to the mechanical-chemical-biological treatment plant system for further processing. The resulting solid substance is fed from the carbonator 3 into the cooled screw conveyor 11, driven by motor 17 and cooled by cooling water 7 before finally being transported to the storage tank 12.

Example 2

[0018] The process is the same as in Example 1, using sludge with a dry matter content of 90% and 10% water content. The alkaline carbonizer is used in an amount of 5% based on the dry matter of the municipal sludge, consisting of 1.4% KHCO3 and the rest up to 100% from cellulose biomass. The working temperature in the thermal carbonizer is 580°C.

Example 3

[0019] The process is the same as in Example 1, but sludge with a dry matter content of 80% and 20% water content is used. The alkaline carbonizer is used in an amount of 5.4% based on the dry matter of the municipal sludge, consisting of 0.5% KOH and the rest up to 100% from biomass from lignocellulose and straw. The working temperature in the thermal carbonizer is 520°C.

Example 4

[0020] The process is the same as in Example 1, the sludge used having a dry matter content of 87% and a water content of 13%. The alkaline carbonizer is used in an amount of 5.2% relative to the dry matter of the municipal sludge, with a composition of 1.2% Na2CO3 and the rest up to 100% biomass consisting of cellulose and sawdust. The working temperature in the thermal carbonizer is 555°C.

[0021] In all examples, the device operates in continuous mode. The method of processing municipal sludge according to the invention yields 65% to 75% of carbonized solid substance (per unit of raw material used - dried municipal sludge) with a carbon content of 35% to 55% (bound and unbound).

[0022] The method and the device for carbonization of municipal sludge according to the technical solution can be used for ecological and efficient disposal of this sludge. The product obtained by carbonization of municipal sludge can be used as a raw material for industry and agriculture.

List of reference symbols

[0023] 1 Inlet 2 Hopper with extruder and degassing 3 Thermal carbonizer 4 Dosing screw 5 First temperature zone I of the thermal carbonizer 6 Second temperature zone II of the thermal carbonizer 7 Cooling water 8 Motor for the screw drive of the thermal carbonizer 9 Cooled condenser 10 Mechanical-chemical-biological treatment plant 11 Screw for cooling and removal of the solid carbonized substance 12 Container for solid carbonized substance 13 Liquid phase that is returned to the treatment system 14 Gaseous phase that is returned to the treatment system 15 Control electronics unit 16 Motor for the dosing screw 17 Motor for the screw for cooling and removal of the carbonized substance

Claims (2)

1. Device for thermal carbonization of municipal sludge, characterized by an inlet (1) for dosing dried municipal sludge and an alkaline carbonizing agent, a hopper (2) with an extruder and degassing, a dosing screw (4) with a motor (16) opening into the space of the thermal carbonator (3) for carbonization of the incoming dried sludge, and equipped with electric heating of the internal space through the outer shell of the thermal carbonator (3) and a screw driven by a motor (8) for moving the carbonated mixture through the space of the thermal carbonator (3), which consists of electrically heated first (5) and second (6) temperature zones, at the end of the first temperature zone (5) there is the discharge of the gas phase from the thermal carbonator (3) through a pipe into a cooled condenser (9) for condensing part of the gas phase, and at the end of the second temperature zone (6) there is an outlet for discharging the resulting carbonized solid substance from the thermal carbonizer (3) into a screw conveyor (11) with motor (17) and cooling by cooling water (7), at the end of the screw conveyor (11) there is the outlet of the cooled solid carbonized substance and it flows into a container (12), wherein the cooled condenser (9) with the condensed gas phase from the thermal carbonizer (3) is connected to a mechanical-chemical-biological treatment plant (10) for separating the liquid (13) and gaseous (14) components, which are fed from the treatment plant (10) back into the system of the mechanical-chemical-biological treatment plant for further processing. 2. Device according to claim 1, characterized by an alkaline carbonating agent consisting of an alkaline mixture containing alkaline hydroxides, hydroxides of alkaline earths, alkaline carbonates, carbonates of alkaline earths, alkaline bicarbonates, bicarbonates of alkaline earths or a mixture thereof with a content of 0.1% to 1.5% by weight and the remainder up to 100% by weight consisting of biomass containing lignocellulose and/or cellulose in the form of grains, semolina, sawdust, fibers or waste paper.