GB2310485A

GB2310485A - Waste disposal unit

Info

Publication number: GB2310485A
Application number: GB9603964A
Authority: GB
Inventors: Howard Morgan Clarke
Original assignee: Morgan Automation Ltd
Current assignee: Morgan Automation Ltd
Priority date: 1996-02-24
Filing date: 1996-02-24
Publication date: 1997-08-27
Anticipated expiration: 2016-02-24
Also published as: GB2310485B; GB9603964D0

Abstract

A waste disposal for consuming medical waste using electric resistor heating unit has a housing 104 cooled by a water jacket 105, with a stainless steel lining 106 of the housing. The lining is cylindrical, with top and bottom plates 107,108 having a top opening 109 for loading waste and a bottom opening 110 for discharge of destroyed waste. Top and bottom water cooled plugs 111, 112 close the respective openings 109,110. The plugs have connections 113 for cooling water flow to and from them and they have graphite insulation blocks. Extending between the openings 109,110 is a molybdenum sleeve 120, defining with plug facings 115, a destruction chamber 103. A pair of inlet and outlet ducts 122,123 open into the chamber just below the level of the top plug facing 115 to provide access to the chamber respectively for purging/cooling air flow and for evacuation. The ducts are positioned in an upper part of the sleeve, which is above a heating element 102. An insulating graphite cylinder 124 surrounds the heating element 102. Waste can be loaded into the chamber in a disposable plastics container 128.

Description

WASTE DISPOSAL UNIT The present invention relates to a waste disposal unit, particularly though not exclusively for medical waste.

Our Patent Application No. 2,289,324, published on 15th November 1995, discloses the use of a plasma arc in a chamber for destruction of waste.

In seeking an alternative means for heating a waste disposal unit in which medical and like waste including stainless steel can be destroyed, we encountered the difficulty in using ohmic heating that stainless steel melts at such a high temperature - of the order of 15000C - as to render attainment of the temperature in the unit without excessive insulation and high power consumption very difficult. However we were surprised to discover that stainless steel in typical medical waste does in fact melt at a lower temperature of the order of 12500C. We believe that this is due to the take up of carbon into the steel from the waste, which includes organic material, particularly packaging.

Accordingly our improved waste disposal unit comprises: a destruction chamber; means for ohmic heating of the chamber; means for evacuating the chamber; means for controlling the temperature of the chamber; whereby the waste in the chamber can be heated to a first temperature to destroy any pathogens, a second temperature to reduce residual organic material to graphitic state and a third temperature less than the normal melting point for stainless steel for melting the stainless steel in the presence of the graphitic material residue, the destruction chamber being evacuated during the heating to at least the second and third temperatures.

Preferably the unit will include means for removal of poisonous gases from the evacuation means. This may be a gas incinerator or a chemical filter.

In order to enhance the useful life of the ohmic heating elements, they are preferably provided in the unit in a void which is separately evacuable. In one embodiment, the heating elements void is adapted to remain evacuated after the destruction chamber has been opened for discharging of ash from the destruction process. This enables the well insulated elements to cool slowly, whilst remaining in a vacuum protecting them from atmospheric oxidation.

For cooling of any remains of the waste, ie ash, subsequent to its destruction, means will normally be provided for purging of the destruction chamber with air.

The cooling air flowing from the chamber will preferably be passed through the poisonous gas removal means.

To help understanding of the invention, two specific embodiments thereof will now be described by way of example and with reference to the accompanying drawing, in which: Figure 1 is a cross-sectional side view of a first waste disposal unit of the invention, Figure 2 is a plan view of the unit on the line II-II in Figure 1 and Figure 3 is a view similar to Figure 1 - though more diagrammatic - of a second waste disposal unit of the invention.

The waste disposal unit shown in Figures 1 and 2 comprises a housing 1. Within this is arranged a hollow, stainless steel sleeve 2 providing a jacket of water 3.

Next within the water jacket is an air gap 4 and a right circular cylinder of graphite 5 with a molybdenum sheet lining 6. On the inside of the lining is mounted via ceramic stand-offs 7 a serpentine molybdenum heating element 8. Across the bottom of this structure is a base 9 having the same general construction. A removable, molybdenum lined graphite lid 10 is supported over the top of the graphite cylinder 5. The lid has its own water jacket top 12 spaced from graphite lid 10 by an air gap 13. Means not shown is provided for securing the lid closed, whereby a seal 14 at the abutment of the water jackets 3,12 is provided for closing the unit. Also not shown is means for circulating water in the water jackets for their cooling.

Shown diagrammatically are supports 11 between the graphite walls 5,10 and the water jackets 3,12.

A rim 15 extends in from the molybdenum lining 6 at the top of the cylinder 5 for support of an inner crucible 16 of molybdenum via a lip 17 on the crucible. Centrally above the crucible is a small aperture 18 for withdrawing gas from the crucible. A duct 19 from the aperture leads to a vacuum pump 20, shown diagrammatically. Gas drawn through the pump is passed through a filter 21, to remove any gases liable to be harmful if released into the atmosphere.

A temperature sensor 22 is provided in the lid for measuring the temperature of the inside of the crucible.

The sensor is connected to a control unit 23 for controlling the vacuum pump and supply of current to the heating element 8.

In use, the lid is closed on the crucible filled with medical waste. Typically, this can include potentially pathogenic samples, plastics utensils and containers, cardboard packing, glass ampules, and stainless steel syringe needles.

The waste is destroyed in the following sequence: I. The crucible is heated to 1500C, by the element 8, for sufficient time to allow the biological, pathogenic material to be destroyed. This is carried out without the application of vacuum in order to avoid drawing pathogens from the crucible. Alternatively, vacuum can be applied during this step, provided the filter 21 can render harmless the gas passing through it.

II. The temperature is then raised to 3000C, whereupon the organic material in the waste degrades essentially to graphite and ash. At this temperature, the vacuum is applied to avoid oxidation not only of the graphite formed in the crucible, but also of the graphite walls and the heating element. It should be noted that whilst there is no specific connection to the evacuation duct 1 of the spaces in the unit, except that in the crucible. However, the air space around the element becomes evacuated, as do the air gaps 4,13 because neither the crucible nor the lid are hermetically sealed to the molybdenum lining of the graphite cylinder 5. The degradation of the organic material to graphite is gradual, consequently the temperature is held at 3000C for a period of the order of ten minutes.

III. The temperature is then steadily raised to 12500C. In the process, the glass in the waste waste melts as do any low melting point metals present. At the elevated temperature, the stainless steel absorbs atomic carbon from the graphitic material. In the process, it changes state to a carbon steel alloy having a melting point below 12500C.

IV. Finally after sufficient time for the steel to be fully melted, the heating elements are switched off and the unit is allowed to cool. Once the temperature is sufficiently low for the risk of oxidation of the molybdenum and graphite components to be avoided, a purging air stream is allowed to flow through the unit by releasing the seal 14. The purging air is passed through the filter 21 as a precaution. Once the entire unit has cooled to room temperature, the lid can be opened and the remains of the waste disposed of as if it were non-dangerous, which it now is.

Turning now to Figure 3, the unit is constructed to allow: 1. Separate evacuation of the space 101 containing the heating element 102; 2. Top loading and bottom discharging of the destruction chamber 103.

This arrangement permits the destruction chamber as such to be opened whilst the heating element space is still cooling under vacuum. In turn this speeds the cycle time for destruction of succeeding batches of waste material.

The unit of Figure 3 has a housing 104 cooled by a water jacket 105, which is in the form of an array of cooling tubes in contact with a stainless steel lining 106 of the housing. The housing is circularly cylindrical, with top and bottom plates 107,108. Centrally of each of these, there is an opening; the top opening 109 is for loading waste and the bottom opening 110 is for discharge of destroyed waste. Top and bottom water cooled plugs 111, 112 are provided for closure of the respective openings 109,110.

The plugs have connections 113 for cooling water flow to and from them. At their inner sides, they are provided with graphite insulation blocks 114 and molybdenum facings 115.

At their outer sides, the plugs have flanges 116, abutting local flanges 117 of the housing 104 at permanently cool regions which enable conventional seals 118 to be installed between the plugs and the housing.

Extending between the openings 109,110 is a molybdenum sleeve 120, defining with the plug facings 115, the destruction chamber 103 as such. The plugs, at their facings 115 are a tight fit in the sleeve, to restrict waste or its ash from leaving the chamber. A pair of inlet and outlet ducts 122,123 open into the chamber just below the level of the top plug facing 115 to provide access to the chamber respectively for purging/cooling air flow and for evacuation. These fixed ducts avoid the need for access through either end plug. They are positioned in an upper part of the sleeve, which is above the heating element and not directly radiantly heated by it.

Surrounding the sleeve 120 within an insulating graphite cylinder 124, the heating element 102 is provided.

The toroidal space 101 for the element is closed and separately evacuable via a duct 127 connected to the vacuum pump via further ducting - neither shown - so as to enable a vacuum to be maintained around the heating element with the destruction chamber being open.

As shown, waste can be loaded into the chamber in a disposable plastics container 128, whose use regulates the load of waste material loaded into the unit at one time.

The operation of the second unit is essentially similar to that of the first, at least as regards heating in three steps after loading of the waste into the chamber in the container 128 via the top opening 109. After the high temperature has been retained for sufficient time for destruction of the waste and after the destruction chamber has dropped to a temperature at which it will not be oxidised itself, cooling air can be introduced via the duct 122 whilst the heating element space remaind evacuated to avoid oxidation of the still hot element. The air cooling then enables withdrawal of the bottom plug 112 from the bottom opening 110 and removal of the ash left from the destroyed waste. If necessary, a further destruction cycle can immediately be initiated before the heating elements have fully cooled.

Claims

CLAIMS:

1. A waste disposal unit comprising: a destruction chamber; means for ohmic heating of the chamber; means for evacuating the chamber; means for controlling the temperature of the chamber; whereby the waste in the chamber can be heated to a first temperature to destroy any pathogens, a second temperature to reduce residual organic material to graphitic state and a third temperature less than the normal melting point for stainless steel for melting the stainless steel in the presence of the graphitic material residue, the destruction chamber being evacuated during the heating to at least the second and third temperatures.

2. A waste disposal unit as claimed in claim 1, including means for removal of poisonous gases from the evacuation means.

3. A waste disposal unit as claimed in claim 2, wherein the poisonous gas removal means is a gas incinerator.

4. A waste disposal unit as claimed in claim 2, wherein the poisonous gas removal means is a chemical filter.

5. A waste disposal unit as claimed in any preceding claim, wherein the ohmic heating means are contained in a separately evacuable void.

6. A waste disposal unit as claimed in claim 5, wherein the separately evacuable void is adapted to remain evacuated after the destruction chamber has been opened for discharging of ash from the destruction process.

7. A waste disposal unit as claimed in any preceding claim, including means for purging of the destruction chamber with air.

8. A waste disposal unit as claimed in claim 7 as appendant to any one of claims 2 to 6, including means for direct purging air to pass through the poisonous gas removal means.

9. A waste disposal unit as claimed in any preceding claim, wherein the destruction chamber is surrounded by sleeve of graphite, preferably with a molybdenum lining.

10. A waste disposal unit as claimed in claim 9, including a water jacket surrounding the graphite sleeve.

11. A waste disposal unit as claimed in any preceding claim, having top and bottom insulation including graphite blocks and water cooling.

12. A waste disposal unit as claimed in any preceding claim, including: an outer housing with top and bottom openings and top and bottom plugs therefor, respectively for loading of waste and removal of ash, flanges on the housing and the plugs at permanently cool regions thereof and low temperature seals at the flanges for sealing the destruction chamber.

13. A waste disposal unit as claimed in claim 12, including inlet and outlet ducts opening into an upper part of the destruction chamber below the top plug to provide access to the chamber respectively for purging/cooling air flow and for evacuation.

14. A waste disposal unit as claimed in claim 13, wherein the inlet and outlet ducts are positioned above the ohmic heating means.

15. A waste disposal unit as claimed in any preceding claim, including a disposable plastics container for the waste material.

16. A waste disposal unit substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.

17. A method of disposing of waste in a disposal unit as claimed in any preceding claim, the method including the steps of: I. Heating the destruction chamber to a temperature of the order of 1500C for sufficient time to allow the biological, pathogenic material to be destroyed; II. Heating the destruction chamber to a temperature of the order of 3000C, whereupon the organic material in the waste degrades essentially to graphite and ash and evacuating the destruction chamber for a period of the order of ten minutes; III. Raising the temperature to the order of 12500C; IV. Allowing the unit to cool and applying a purging air stream.

18. A method of disposing of waste substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.