FR2721690A1 - Disposal of solid hospital wastes by incineration - Google Patents

Abstract

A process and installation are claimed for the heat treatment of solid combustible wastes, particularly from hospitals. Solid waste (22) is placed in a gasification chamber (1) where a gasification agent containing oxygen is added and a gasification zone (3) set up. As solids are gasified, further material drops into the zone. Gaseous products are withdrawn (6). The gas is added in two parts (4 and 5), one stream passing through solids (24) moving towards the gasification zone, and the other being fed directly to the zone (25). Waste is charged to the incinerator directly in its disposable containers. Gaseous products from the gasification zone are drawn into a post combustion chamber (7) where an excess of secondary oxidising gas (9) is added. This gas is preheated by heat exchange with gaseous products (15). Products are passed through a bed of absorbent material (37) to remove noxious components. Temperatures in the gasification zone and post combustion chamber are regulated by adjustment of the gas feed rate. At the end of the cycle when the gasification chamber is almost empty hot gas is added to thermally treat the vessel walls and disinfect them.

Description

DESCRIPTION
The present invention relates to a method and a device for heat treating, in an ecological manner, hospital waste and other waste containing fuel.

 Waste disposal must ensure complete incineration of the fuel at high temperature, incombustible residues and smoke must be free of germs, dangerous compounds and odors.

Currently, most of the hospital waste is incinerated with household waste in incineration plants. This process has the disadvantage of presenting a great risk of contamination during the transport of hazardous contaminated waste, or of entailing high costs of disinfection before transport.

 The incineration of such waste directly at the place of collection (in clinics, hospitals, etc.) could significantly reduce the cost and the risk of contamination linked to transport. However, small devices (ovens) for incinerating waste are usually perfectible and do not meet the requirements in terms of smoke cleanliness, reliability, and convenience of use.

They pollute the environment in particular during ignition and extinction, as well as when reloading waste in the oven, due to the significant formation of gas caused by ignition of the waste and combustion . The operation of such incinerators can be interrupted by variations in the composition and properties of the waste (humidity, ash content, etc.), which leads to an increase in harmful discharges.

 FR-A-2 649 782 describes a process for the incineration of solid hospital, household and industrial waste, which is intended to exclude pollution of the environment, and in which stages of ignition, pyrolysis, combustion and cooling are ensured in sequence under continuous piloting. The overload caused by the introduction of a new batch of waste into the oven is prevented by controlling the air supply and the operation of the burners as a function of the pressure in the oven and the temperatures in the oven and in a chamber. afterburner. The main drawbacks of this process are that it consumes a lot of energy and requires a complex installation, as well as additional fuel (combustible gas) to maintain the pyrolysis and combustion.

 EP-A-0 251 269 describes a process and a reactor for the gasification of solid fuels followed by the combustion of gaseous products, using a gas generator for the gasification of solid fuels such as wood, coal, fuel in briquettes, household waste, etc ..., followed by a burner for the combustion of gaseous products directly after gasification in the oven. To improve the thermal efficiency of the combustion of the aforementioned fuels, the primary air injected into the gasification zone and the secondary air supplied to the burner are heated by the heat released by the gasification. The air is heated by passing the primary air and the secondary air through passages provided in a multiple wall of the gasification chamber.

 This principle excludes overloads when using fuels such as coal or briquettes, since new quantities of fuels are supplied to the gasification zone continuously as the previous quantities are consumed. However, when the material to be treated consists of waste, it does not regularly feed the gasification zone because, due to their low density, the waste loaded in the gasification chamber can adhere to the walls of the chamber. Another possible cause of burner overload, the tars emerging from the gasification zone may condense on the colder waste descending towards it and thus agglomerate the waste. The condensation of tars also has the effect of degrading the friability of the waste and its permeability to gases.

 The process according to EP-A-0 251 269 has the further disadvantage of transferring heat from the gasification zone since this can result in the extinction of the combustion of a fuel with a low calorific value, for example wet. This leads to constraints with regard to the composition of the fuel.

 The aim of the present invention is to propose an ecological heat treatment, more particularly a gasification for incineration, of hospital waste and other solid waste containing fuels, ensuring reliable operation regardless of the experience of the personnel and for a wide range of compositions, calorific values, and hygrometry of waste, this process must more particularly avoid to a large extent the agglomeration of waste in the gasification chamber upstream of the gasification zone.

According to the invention, the method for hot treating solid waste containing fuels, such as hospital waste, comprising the steps according to which
- we load the waste in a
gasification
- a gasification zone is established in the
gasification chamber by introducing an agent
of gasification containing oxygen in the
gasification area so the waste gets
move into the gasification chamber in
succession to the gasification zone for y
be successively carbonated,
- gaseous gasification products are removed from
the gasification zone,
is characterized in that the gasification agent is introduced into the gasification chamber in a distributed manner, dividing it into at least a first and a second part; the first part being injected into the gasification chamber to pass the waste passing towards the gasification zone together with the movement of the waste in the chamber, and the second part of the gasification agent being sent through the gasification zone only.

 According to a second aspect of the invention, the device for implementing the method, comprising a gasification chamber adapted to receive solid waste containing fuel such as hospital waste, admission means for introducing a gasification agent into the gasification chamber and outlet means for withdrawing gaseous gasification products from the gasification chamber, is characterized in that the inlet means for introducing a gasification agent are means for supplying the gasification agent so distributed in the gasification chamber, arranged relative to the outlet means for gaseous products so that a flow of said gasification agent is divided into at least a first and second part, the first part of the gasification agent passing successively through the waste moving through the gasification chamber to the gasification zone , and the second part passing through the gasification zone only.

 Thanks to the invention, the gasification chamber is subdivided into a drying zone and a gasification zone. A gasifying agent, such as air, is introduced into the gasification chamber in a distributed manner, so that a first part enters the gasification chamber clearly upstream of the gasification zone, and establishes there. a drying area. The first part of the gasification agent flows successively through the drying and gasification zones together with the movement of the waste along the chamber. A second part of the gasification agent only crosses the gasification zone, in which the incombustible solid products such as ash, dross etc. are deposited. The waste passes through the chamber and feeds the gasification zone as it is consumed by the process. The gaseous products are preferably sent to an after-combustion chamber through orifices in a wall separating the gasification and post-combustion. In the post-combustion chamber, they are completely oxidized in the presence of an excess of secondary air. The fumes are evacuated from the post-combustion chamber. The flow of the gasifying agent through the drying zone in accordance with the movement of the waste through the chamber promotes said displacement, entrains towards the gasification zone the aqueous vapors and other volatile components which are released in the zone of drying, and prevents the tars produced by the gasification from driving back to the drying area and condensing there. Such condensation could cause the waste being treated to agglomerate, and affect its porosity and friability.

This could compromise the delivery of waste, and even the gasifier, to the gasification area.

 The process can use air as a gasifying agent. However, when treating dry waste with high calorific value, it is also possible to inject steam into the gasification agent so as to reduce the temperature in the gasification zone.

 The method according to the invention is particularly effective for being implemented in small and highly reliable incinerators for thermally treating waste directly at the place of its production, for example in a hospital.

 To reduce the risk of contamination by germs or dangerous chemicals present in the waste, the waste can be loaded directly into disposable containers (provided that these are flammable, for example the usual polyethylene bags), these containers also being incinerated along with the waste.

 The displacement of the waste towards the gasification zone can be promoted by a corresponding design and size of the gasification chamber, for example by making it flared downwards. You can also activate the movement by a sort of agitator.

 The volume of the post-combustion chamber is chosen so that when operating at the nominal capacity of the incinerator, the retention of smoke in the chamber exceeds the standard duration required, and under a temperature and an oxygen concentration exceeding the prescribed standard values. These standard times and values are those determined to guarantee the elimination of organic pollutants.

 The process can be initiated by a thermal pulse applied to the waste in the gasification zone and / or in the gasification agent flow by means of an additional heat source, for example an electric heating, the operation of which is interrupted when the gasification process has been established stably. Gasification and combustion are controlled by regulating the consumption of gasification agent and secondary air and by redistributing the gasification agent and secondary air between the corresponding intake orifices, as a function of the temperatures in the zone of gasification and in the afterburner. The temperatures are kept within the range, the lower limit of which is defined by the need to prevent the release of organic compounds, in particular dioxynes, in dangerous concentrations.

The upper temperature limit can be defined by the thermal resistance of the materials constituting the incinerator. When the temperature in the gasification zone tends to exceed the prescribed upper limit, the feed rate of the gasification agent is reduced. If the temperature in the post-combustion chamber exceeds the upper limit, the secondary air supply rate is increased.

If the waste has a low calorific value, the additional heat source can be kept in operation by regulating its power, even after initiation of the gasification process, so as to maintain the temperature above the lower limit.

 The controls described above can be provided automatically. To this end, the incinerator can be provided with a control device comprising probes for temperature measurements in the gasification and post-combustion chambers, and means for controlling the corresponding feed rates and the distribution of the gasification agent and secondary air on the various means of admission to the chambers of the incinerator as a function of these temperatures. However, for particular wastes which are known to remain within certain limits of composition and properties, such control can result from a factory setting, by simple mounting of corresponding gas conduits, having correlated cross sections.

 To extend the possibility of applying the process to various wastes, it is possible to preheat the secondary air supplying the post-combustion chamber by means of the heat recovered in the fumes generated in the post-combustion chamber. Heat recovery can be achieved by means of a heat exchanger mounted either directly in the afterburner or downstream from it in the flue gas flow path. Such preheating of the secondary air makes it possible to incinerate waste which gives off gases with low calorific value during gasification.

 The treatment of waste containing dangerous additives, for example chlorine or sulfur, can also be followed by a step of purifying the fumes from the post-combustion chamber and / or the pyrolysis gases withdrawn from the gasification chamber. , to extract harmful gases therefrom using known techniques, for example by passing the gaseous products through one or more layers of limestone or other materials absorbing and neutralizing these pollutants. If the purification step relates to the pyrolysis gases, for example these are passed through a conduit containing said materials and connecting the gasification chamber to the afterburner chamber.

 To reduce the risk of air pollution by particles, the post-combustion chamber can be subdivided into separate volumes connected in series so that the fumes pass through them all successively. one of these volumes is preferably arranged in a cyclone, the duct leading to this volume being arranged to ensure a circular flow of gases therein. Such a cyclone rids the gases of dust particles.

 Before switching off the incinerator, when its gasification chamber is substantially empty of waste with the exception of the part of this chamber where the gasification zone is located, a supply of gasification agent is distributed so that the internal surfaces of the gasification chamber are heat treated for the purpose of disinfection. For this, the gasification chamber is provided with an inlet for hot gasification agent. The heating of such a gasification agent can be provided in the same heat exchanger as that preheating the secondary air.

 To ensure a regular draft, the incinerator may be provided, in addition to a chimney for the fumes emerging from the combustion chamber, with a draft assistance device, for example an extractor fan or an ejector. This maintains a slight negative pressure in the gasification and post-combustion chambers, which will prevent gas leaks from them.

 Other features and advantages of the invention will emerge from the description below, relating to non-limiting examples.

To the accompanying drawings
- Figure 1 is an elevational diagram of an incinerator according to the invention; and
- Figure 2 is a diagram similar to Figure 1, but on a slightly reduced scale and relating to a variant, with a detail II seen from above.

 The incinerator of FIG. 1 comprises a gasification chamber 1 elongated vertically having an upper opening which is normally closed by a cover 21. When the cover is open, it is possible to introduce into the gasification chamber 1 waste 22, such as hospital waste in disposable plastic containers.

 The bottom of the gasification chamber is defined by a grid 8 through which the gasification chamber 1 is in fluid communication with an afterburner chamber 7, which in turn is in fluid communication with the outside through a chimney 23 for the fumes.

 The gasification chamber is provided with two intake ports 4, 5 for a gasification agent, namely air in the example. A first orifice 4 is relatively distant from the grid 8, while a second orifice 5 is closer to the grid 8. The flow of gasification agent in the gasification chamber is thus divided into a first part 24, going from the intake orifice 4 to the grid 8, and a second part 25 going from the second intake orifice 5 to the grid 8.

 An electric heater 11 is mounted in the post-combustion chamber 7 just below the grate 8.

 We will now explain the gasification process. The waste 22 being loaded into the gasification chamber 1, the heater 11 is operated to initiate the heating of the lower part of the waste 22, and the gasification agent is introduced through the intake ports 4 and 5. This starts the gasification of the lower part of the waste, after which the heater 11 can be switched off. As the successively lower parts of the waste are gasified, the other parts successively move by gravity towards the grid 8. A gasification zone 3 which is substantially stable is established in the gasification chamber against the grid 8, and the second inlet port 5 for the gasification agent is positioned so that the second part 25 of the gasification agent only flows through the gasification zone 3. On the contrary, the inlet 4 is positioned so that the first part 24 of the gasification agent enters the gasification chamber well above the gasification zone 3, which establishes a drying zone 2 in which the volatile components, including water, released from the waste, are captured by the first stream of gasification agent and entrained with it in the gasification zone 3.

 The gasification gas products 6 emerging from the gasification zone 3 flow through the grid 8 into the post-combustion chamber 7. An intake orifice 9 is provided in the post-combustion chamber 7 in the vicinity of the grid 8 for injecting into the post-combustion chamber 7 a secondary oxidizing gas, such as air, so as to burn the gaseous gasification products in the post-combustion chamber. When an incineration session begins, the heating 11 serves not only to initiate the gasification but also to initiate the combustion of the gasification gas products 6. The secondary air is introduced in an amount more than stoichiometric so that the fumes 10 in the post-combustion chamber 7 contain excess oxygen in proportion corresponding to the standards for gas decontamination. For better incineration of gaseous gasification products, secondary air, before being introduced into the post-combustion chamber combustion 7 through the inlet 9, is heated through a heat exchanger 15 mounted in the post-combustion chamber 7 in the vicinity of its outlet. In the exchanger 15, the secondary air recovers heat from the fumes from the post-combustion chamber 7.

 The gasification chamber 1 is further provided with an additional inlet orifice 16 for introducing hot gasification agent 17 at a point remote from the grid 8, in the vicinity of the cover 21.

 The orifice 16 is supplied with gasification agent in the form of hot air available at the outlet of the heat exchanger 15, like the secondary air supplying the intake orifice 9.

 All the gas intake orifices 4, 5, 9, 16 are equipped with flow control means 14 connected to an automatic pilot device 12 which also controls the operation of the heating 11, and which is connected to temperature probes 13, one in the gasification chamber 1 and the other in the post-combustion chamber 7.

 The flow control means 14 of the additional inlet port 16 is controlled to supply hot gasifying agent through the port 16 when the gasification chamber is almost empty because a batch of waste has been almost completely gasified, so as to disinfect the internal surfaces of the gasification chamber by heat. But as the gasification chamber is not yet completely empty, gaseous products continue to emerge from the gasification zone and to be burnt in the post-combustion chamber, so that the heat exchanger 15 remains capable produce hot gasifier for port 16.

 A draft assistance device 18, in the form of an ejector, is mounted at the outlet of the post-combustion chamber 7 to produce a definite vacuum in the whole of the incinerator, which avoids the risks noxious gas leak from the incinerator.

 A filter 37, consisting for example of one or more layers of limestone particles, is also mounted in the outlet of the afterburner chamber 7.

 In the example of FIG. 2, which will only be described for its differences from that of FIG. 1, the post-combustion chamber 7 is subdivided into two volumes 41, 42, which the fumes 10 pass through successively before leaving the chamber 7. The downstream volume 42 is arranged in a cyclone with a vertical axis so as to dust off the fumes. The gas conduit 43 through which the upstream volume 41 adjacent to the grid 8 communicates with the downstream volume 42 at an outlet opening directed in the circumferential direction of the volume 42 to generate the cyclone effect. The conduit 43 opens at the top of the volume 42. An outlet conduit 44 allowing the fumes to exit from the volume 42 has an opening close to the base of the volume 42 and extends axially upward through the volume 42. outer surface of the duct 44 serves as a rotation guide for the fumes 10 in the volume 42 around the duct 44. The heat exchanger 15 is placed downstream of the volume 42, between the latter and the ejector 18. A filter such that 37 (Figure 1) has not been shown in Figure 2 but could also be provided.

A sample of waste, imitating the composition of hospital waste (from the waste analysis of CHERNOGOLOVKA hospital, in the Moscow region,
Russia) consisting of
- textile 24% by weight
- paper 28%
- 12% cardboard
- 9% polyethylene
- rubber 2%
- aluminum sheet 2%
- 7% glass, and
- water 16%
was loaded into the gasification chamber of a laboratory incinerator produced in the form of a vertical cylinder subdivided by a metal grid into an upper gasification chamber and a lower post-combustion chamber. The secondary air heat exchanger was placed in the lower part of the post-combustion chamber. An electric heater was placed in the upper part of the post-combustion chamber, under the grate, to initiate the gasification process in the gasification chamber and ignite the gaseous products therefrom. There was also an intake port for introducing secondary air.

 In the lower part of the gasification chamber there was above the grid an inlet orifice to introduce a gasification agent (primary air) into the gasification zone, and there was in the upper part of the same chamber a second intake port for introducing primary air into the gasification chamber for the forced drying of waste.

 The mass and density of the charged mixture were 1.65 kg and 190 kg / m3, respectively. After applying the thermal pulse by means of the heating for ignition, the primary air was sent to the gasification chamber and the secondary air to the post-combustion chamber. With flow rates of 1.5 1 / second for the supply of primary air and 0.75 1 / second for the supply of secondary air, the treatment time was 30 min. The temperatures in the gasification zone and in the post-combustion chamber were approximately 700 to 800 "C and respectively 900 to 10000C; the temperature of the fumes leaving the post-combustion chamber (behind the heat exchanger heat) was less than 1700 C. The post-combustion chamber discharges contained no visible dust and had no odor. The weight of the non-combustible residues consisting of molten glass, foil and ash was 0.21 kg.

 The average ratio of air consumption through the two primary air intake ports in the gasification chamber was 2: 1, the highest consumption of gasification agent corresponding during most of the process to the consumption through the inlet in the gasification zone. But at the final stage of the process, this ratio was reversed to ensure disinfection of the chamber. Thus, in this laboratory incinerator, the intake ports 4 and 16 of FIG. 1 were in fact a single port.

Claims (22)

 1. Method for hot treating solid waste containing fuels, such as hospital waste, comprising the steps according to which  - the waste (22) is loaded into a  gasification (1);  - a gasification zone (3) is established in the  gasification chamber by introducing an agent  of gasification containing oxygen in the  gasification area so the waste gets  move into the gasification chamber in  succession to the gasification zone for y  be successively carbonated,  - gaseous gasification products are removed,  (6) of the gasification zone (3),  characterized in that the gasification agent is introduced into the gasification chamber in a distributed manner, dividing it into at least a first and a second part, the first part (24) being injected into the gasification chamber (1) to pass the waste (22) move to the gasification zone (3) together with the movement of the waste in the chamber (1), and the second part (25) of the gasification agent being sent to through the gasification zone (3) only.  2. Method according to claim 1, characterized in that steam is introduced into the gasification agent supplying the gasification zone (3).  3. Method according to claim 1 or 2, characterized by a step of purifying the gaseous gasification products.  4. Method according to claim 1, 2 or 3, characterized in that the waste (22) is loaded into the gasification chamber (1) directly into disposable containers.  5. Method according to any one of claims 1 to 4, characterized in that before completing a gasification operation, when the gasification chamber is substantially empty of waste with the exception of the part of this chamber where is located the gasification zone (3), a hot gasification agent (17) is injected into the gasification chamber so that internal surfaces of the gasification chamber are heat treated for disinfection.  6. Method according to claim 5, characterized in that before injection, said hot gasifying agent is heated by heat produced by the combustion of the gaseous products of the gasification.  7. Method according to any one of claims 1 to 6, characterized in that the gaseous gasification products (6) removed from the gasification zone are sent, in an afterburner chamber (7) into which a gas is injected. secondary oxidant.  8. Method according to claim 7, characterized in that the secondary oxidizing gas is injected in amounts more than stoichiometric.  9. Method according to claim 7 or 8, characterized in that the secondary oxidizing gas (9) is preheated with heat recovered from the fumes (10) formed in the post-combustion chamber (7).  10. Method according to any one of claims 7 to 9, characterized in that the said fumes are purified in order to extract the harmful gases therefrom.  11. The method of claim 3 or 10, characterized in that said purification step comprises the step of passing gaseous products through at least one layer of material absorbing or neutralizing harmful gases.  12. Method according to any one of claims 7 to 11, characterized in that the temperature is regulated in the post-combustion chamber (7) by increasing the flow of secondary oxidizing gas when this temperature tends to become too high.  13. Method according to any one of claims 1 to 12, characterized in that the temperature is regulated in the gasification zone by reducing the flow of gasification agent when this temperature tends to become too high.  14. Device for implementing a method according to any one of claims 1 to 13, comprising a gasification chamber (1) adapted to receive solid waste (22) containing fuel, such as hospital waste, means of inlet (4,5) for introducing a gasification agent into the gasification chamber and outlet means (8) for withdrawing gaseous gasification products (6) from the gasification chamber, characterized in that the means for inlet for introducing a gasification agent are means for distributing the gasification agent in a distributed manner in the gasification chamber (1), the admission means (4,5) in the gasification chamber being arranged relative to the means outlet (8) for gaseous products so that a flow of said gasification agent is divided into at least a first and second part, the first part of the gasification agent passing successively ement through the waste going to the gasification zone in the gasification chamber, and the second part passing through the gasification zone only.  15. Device according to claim 14, characterized in that the outlet means (8) of the gasification chamber (1) provide fluid communication between the gasification chamber (1) and an afterburner chamber (7) provided with an inlet orifice (9) for a secondary oxidizing gas, and with an outlet for gaseous products resulting from the combustion of gaseous gasification products.  16. Device according to claim 15, characterized by heat exchanger means (15) mounted to ensure a heat exchange between the combustion fumes and the secondary oxidizing gas flowing towards the inlet orifice (9) for gas secondary oxidant.  17. Device according to claim 15 or 16, characterized in that the post-combustion chamber (7) is arranged so as to be subdivided into at least two volumes (41, 42) successively traversed by the gas flow (10) .  18. Device according to claim 17, characterized in that at least one (42) of the volumes is arranged in a cyclone to dedust the gas flow.  19. Device according to any one of claims 14 to 18, characterized in that it comprises control means (12) connected to probes (13) for measuring temperature in the device and to flow control means (14) for controlling the flow rates through the intake orifices (4, 5, 9) as a function of the temperatures detected by the probes (13).  20. Device according to any one of claims 14 to 19, characterized in that its gasification chamber (1) is provided with at least one additional intake orifice (16) for a heated gasification agent (17), suitable for disinfecting internal surfaces of the gasification chamber (1).  21. Device according to claim 20, characterized in that said additional orifice (16) is located at a distance from the outlet means (8) for gaseous gasification products.  22. Device according to any one of claims 14 to 21, characterized in that it is provided with a draft assistance device (18) such as an extractor fan or an ejector.