US3888194A - Method for incinerating industrial wastage - Google Patents

Abstract

There is disclosed a method for incinerating combustible industrial wastage containing organic nitrogen compounds of a peptide bond, cyan radical, etc. by using a so called fluidized bed incineration furnace. This method uses steps of supplying, the aforesaid wastage together with combustible materials abundant in carbon content, such as pulverized coal, heavy oil, etc., in the fluidized bed to thereby maintain the interior of the fluidized bed in a reductive atmosphere, while reducing nitrogen oxide produced from the combustion of the wastage, whereby nitrogen oxide may be removed as innocuous nitrogen from waste-gas or stack gas.

Description

United States Patent 1191 Kishigami et al.

1111 3,888,194 1 1 June 10, 1975 1 1 METHOD FOR INCINERATING 3.306236 2/1967 Campbell t. 110/8 3,515,381 6/1970 Foch 1 1 .v 110/8 X INDUSTRIAL WASTAGE 3,589,313 6/1971 Smith et a1 v 1 110/8 [75] Inventors: Kunio Kishigami; Hiroshi 3,772,998 11/1973 Menigat 110/8 Kobayashi; Toru Sente; Koichi 3,776,150 12/1973 Evans et a1. 1 10/28 X Sugiyama, all of Yokohama, Japan [73] Assignee: Babcock-Hitachi K.K., Tokyo, Primary Examiner kfenneth Sprague Japan Attorney, Agent, or Firm-Thomas E. Beall, Jr. 2 Fl d: F 2] 1e eb 28,1974 ABSTRACT [21 1 Appl' 446'895 There is disclosed a method for incinerating combustible industrial wastage containing organic nitrogen [30] Foreign Application P i it D t compounds of a peptide bond, cyan radical. etc. by Nov 2L I973 Japan 48430187 using a so called fluidized bed incineration furnace. This method uses steps of supplying. the aforesaid [52] CL n "0/8 F; I [0/28 1 10/49 wastage together with combustible materials abundant l 10/8 6 in carbon content, such as pulverized coal, heavy oil, [5 H CL H F23g etc., in the fluidized bed to thereby maintain the inte- [58] n w of Search n 0/7 R 8 R 18 R 28 J rior of the fluidized bed in a reductive atmosphere, 1 0/119 while reducing nitrogen oxide produced from the combustion of the wastage, whereby nitrogen oxide [56] References Chad may be removed as innocuous nitrogen from waste-gas UNITED STATES PATENTS Stack 2 729,428 1/1956 Milmorc 2. 122/4 x 7 Claims, 3 Drawing Figures 10 I./' I 1 1 1 1 l 1 4 1 1 i 8 1 I 130 19 M 5 0 "2Q 60 i 7 l 1 1 14 5 1 2131 ,5 1 1' 1 i I i 2 1 I 12O /1 1 1 1 l 1 1 19b 6b 17 1 1s 2 1 :15 r 1 p 1 v /1 1 1 9 we 2 PATENTEDJUN 10 I975 FIG.

FIG. 3

METHOD FOR INCINERATING INDUSTRIAL WASTAGE BACKGROUND OF THE INVENTION I. Field of the invention This invention relates to a method for incinerating in a fluidized bed furnace the industrial wastage containing organic nitrogen compounds which produce, upon incineration, a great quantity of nitrogen oxide detri mental to the human body, and more particularly to a method for reducing and removing nitrogen oxide thus produced, by maintaining the interior of a fluidized bed in a reductive atmosphere. thereby minimizing the quantity of nitrogen oxide contained in the combustion waste-gas.

2. Description of the prior art Hithereto, it has been a general practice to use an incineration method for treating muddy industrial wastage, and such incineration has been admitted as the most reasonable method which finds a wide use of this kind. The most common incineration furnace for use to this end is of a fluidized bed type. In the fluidized incineration furnace, air is blown from below through the incombustible fluidizing medium particles placed on a perforated plate provided in the furnace, to fluidize same, while the interior of the fluidized bed is preheated by means such as a burner to a temperature higher than combustion temperatures of the materials to be burnt, and the materials to be burnt are fed into the furnace from its top, whereby the materials to be burnt may be incinerated due to a combustion heat produced from the burning materials themselves. In other words, the fluidized bed furnace as used herein is an incineration furnace using a fluidized bed.

Contained in the recent industrial wastage, particularly in the muddy effluent from various kinds of effluent treating apparatuses are a small amount of sulfur, chlorine and nitrogen in addition to carbon and hydrogen which are combustible matters.

Those elements are not present in the form ofa single substance but as complicated compounds. Those may be generally classified into biological compound such as protein and artificial compounds such as polyamide resin.

The organic nitrogen compounds contained in the industrial wastage such as for instance protein, polyamide resin, sewage sludge, acrylic resin, etc., are present in the form ofa peptide bond (CO. NH), cyan radical (-CN), ammoniacal nitrogen (NH, nitric and nitrous nitrogens (NO;;, NO and the like, and the incineration of such organic nitrogen compounds would leads to the production of nitrogen oxides (NO which are detrimental to a human body and of a quantity which is commensurate to that of nitrogen contained in the materials to be burnt.

Experiments reveal that the aforesaid wastage produces NO,, even when burnt at a temperature as low as 750 to 850C, because of the bonding condition of the nitrogen contained therein. The production of NO is due to the reaction of organic nitrogen compounds contained in the wastage with oxygen, during combustion. Thus, it should be noted that the mechanism of the production of NO, is fundamentally different in its mechanism from a phenomenon. wherein inorganic nitrogen contained in air is oxidized at an elevated ternpcrature to produce NO,.

The nitrogen oxides (NO which are produced due to the oxidation of inorganic nitrogen contained in air during the combustion process in a general type industrial furnace such as a boiler are negligible in quantity in the case of a temperature being below l,()00C, whereas in the case of the temperature being over l,000C, the quantity of nitrogen oxides (NO,] produced is notably increased. This is because nitrogen (N and oxygen (0 in air react with each other at an elevated temperature such as above l,(l()()C according to the following formula, thereby producing NO:

On the contrary, nitrogen oxides (NO produced from the combustion of organic nitrogen compounds contained in muddy wastage exhausted from various kinds of effluent treating apparatuses are not like those which are produced from the oxidation of nitrogen in air at an elevated temperature but those which are produced from the decomposition of organic nitrogen compounds contained in the muddy wastage. Accordingly, nitrogen oxide may be produced at any level of a lower temperature, as far as the muddy wastage is in the range of temperatures, at which it is combustible.

As a result, nitrogen oxides which are produced from the oxidation of nitrogen with oxygen in air during the combustion in the industrial furnaces of a general type may be prevented to some extent from being produced by lowering the combustion temperature to not more than l,000C. In contrast thereto, nitrogen oxides which are produced from the combustion of organic nitrogen compounds may not be prevented from production simply by resorting to a measure to lower the temperature.

Accordingly, it is an object of the present invention to provide a method for incinerating industrial wastage containing organic nitrogen compounds therein, said method being adapted to prevent the production of the nitrogen oxides to a possibly minimized extent.

For a consideration of what is believed to be novel in the present invention, attention is directed to the following description and the claims appended thereto in connection with the accompanying drawings.

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for incinerating industrial wastage, in which air is blown into a furnace from below to fluidize incombustible fluidizing medium particles placed in the furnace, thereby forming a fluidized bed, while said industrial wastage is introduced in the fluidized bed from the top of the fluidized bed incineration furnace which has been preheated to a temperature above a combustion temperature of combustible industrial wastage to be burnt, and then the aforesaid wastage is burnt due to the combustion heat produced from the wastage itself, said method being characterized in that combustible materials abundant in carbon content is supplied together with the aforesaid wastage into the furnace, thereby maintaining the interior of the fluidized bed in a reductive atmosphere whereby the nitrogen oxides produced from the combustion of organic nitrogen contained in the aforesaid wastage may be reduced to an innocuous nitrogen and thus nitrogen oxide may be removed from the combustion waste gas.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a magnified view ofa muddy particle within a fluidized bed incineration furnace, embodying the present invention;

FIGv 2 is a view illustrating the conditions within a fluidized bed incineration furnace embodying the present invention; and

FIG. 3 is a schematic view illustrating an operational system and the cross section of a fluidized bed incineration furnace embodying the invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to providing a method for incinerating industrial wastage containing organic nitrogen compounds, by using a fluidized bed furnace, in which industrial wastage together with ma terials containing a great amount of carbon, such as pulverized coal, heavy oil or the like is charged in a furnace to thereby fluidized the wastage and the carbon abundant material together with fluidizing medium with air, and then the industrial wastage is burnt, while the interior of the fluidized bed (or fluidized layer) is maintained in a reductive atmosphere, whereby the nitrogen oxides (NO,,.) produced from the organic nitrogen compounds contained in the wastage are reduced during the combustion of the wastage, to thereby obtain nitrogen gas (N thus preventing the production of nitrogen oxides.

As is well know, the fluidized bed is provided by blowing air or gas into a furnace from its bottom and fluidizing the fluidizing medium in the form of solid particle layer which is supported on a perforated plate within a furnace. In general, silica base particles (primary constituent SiO such as river sand, which is chemically inactive, are used as a fluidizing medium of a solid particle layer, the particle size thereof being in the range from 0.1 to 2.0 mm. In case sulfur and chlo rine are contained in the wastage and desired to be directly fixed and absorbed within the fluidized bed, it is preferable that chemically active cement clinker parti' cles be used as a fluidizing medium. The composition of cement clinker particles is, for instance, 60 to 70% CaO, 6 to 8% Fe O and 3 to 6 SiO The fluidized bed incineration furnace utilizes a fluidized bed for incineration. The temperature of the fluidized bed is normally in the range from 750 to 850C. In the respect, such a temperature is extremely lower than the temperature (over 1,000C), at which nitrogen oxides are formed by the reaction of nitrogen with oxygen contained in air, as is the cases with industrial furnaces of a general type, such as a boiler. Furthermore, at such a low temperature, the quantity of nitro gen oxides produced according to the reaction of nitrogen with oxygen in air is neglisible.

What is of consequence in this respect is the production of nitrogen oxides due to the combustion of organic nitrogen compounds contained in the wastage, because as has been described earlier, nitrogen oxides may be produced in a great quantity even at a temperature as low as 750 to 850C.

Vigorous reaction may be achieved in the fluidized bed furnace, because the fluidizing solid particle layer consists of particles of a size from 0.l to 2.0 mm and thus presents extremely large contact surface area at the time when the particle layer stands still (e.g., the height of the layer is 500 to 1,000 mm). Accordingly,

even the wastage such as those having poor combustibility, like a dehydrated mudcake (water content: to may be burnt at a very low excessive air ratio l l to 1.3). In case a dehydrated mud'cake having a high water content and containing materials having a high carbon content is burnt in the fluidized bed, the follow ing reaction formulae are considered to take place, because the combustible solid matter in the mud consists essentially of carbon, hydrogen, sulfur and nitrogen;

However, in practice. the wastage particles are maldistributed microscopically to some extent, despite that muddy wastage has been dried. crushed and placed within the fluidized bed. Furthermore, the wastage particles are subjected to combustion at a very small ex cessive air ratio, such that a reductive atmosphere short of oxygen encircles around the small particles of crushed wastage.

Such a condition will be described in more detail with reference to drawings, FIG. 1 is a magnified view of a mud piece b, showing the condition within a fluidized a, microscopically. Mud pieces b float in the fluidizing medium particle group d forming a fluidized bed a, while a mud piece b containing a considerable amount of carbon components forms a reductive atmosphere in its surrounded zone c.

On the other hand, there are present in the fluidized bed gas components such as CH CO, H etc., produced due to decomposition of wastage, and the afore said gas components asist in enhancing the effectiveness of the reductive atmosphere.

The fluidized bed itself has a strong catalytic action. There are contained Fe O and AI O in the aforesaid active fluidizing medium particles or vanadium oxide (V 0 formed by vanadium (V) in the heavy oil in said medium particles, if heavy oil is used for auxiliary burning, and those compounds act as catalysts to accelerate the formation of carbon monoxide according to the following formulae:

C H O C0 H (water gas reaction) In other words, for incineration of mud cake having a high water content, materials abundant in carbon content, such as pulverized carbon, or waste activated carbon, if required, heavy oil are supplied together with muddy wastage in the fluidized bed, or otherwise the mixture of muddy wastage and materials abundant in carbon content may be supplied into the fluidized bed for combustion at a small excessive air ratio, whereby a great quantity of CO is produced in the fluidized bed for selective reduction of nitrogen oxides according to the following formulae:

2N0 CO NO CO In addition, hydrogen produced according to the aforesaid water gas reaction and methane which are produced from hydrocarbon (C,,h,,,) contained in combustible materials in the reductive atmosphere. reduce nitrogen oxides as follows:

Fe O (W MnO, A1 0 V 0 C11 0 and the like are considered to be catalysts adapted to accelerate the above reactions.

Description will now be given by referring to FIG. 2 showing the condition of the interior of a fluidized bed incineration furnace for use in muddy wastage incineration.

In the fluidized bed incineration furnace e, the primary air g of the combustion air is fed into the incineration furnace e from below for fluidizing the fluidizing medium within the furnace 0, thereby forming a fluidized bed k. The fluidized bed It is preheated by means of a burners or the like. Materials abundant in carbon content such as pulverized coal or the like is supplied together with muddy wastage from the top of the furnace e into the fluidized bed It to be fluidized together with the fluidizing medium and incomplete combustion results, whereby the interior of the fluidized bed It is maintained in a reductive atmosphere. Thus, the incineration is carried out in this manner. In this case, there are present in the form of mixture CO, H CH 0 N and CO within the fluidized bed k, such that the formation of the reductive atmosphere within the fluidized bed k may be accelerated.

Furthermore, when the secondary airfis supplied to the upper space over the fluidizing bed in the fornace e, if 1 ()t is Excess Air Factor) in zone] defined by the upper surface of the fluidized bed It and the inlet of the secondary air f, CH and the like which have entered this zone will be decomposed and burnt. The combustion will further proceed in the zone 1' above the zonej, and waste gas it containing CO H O, N and O is exhausted from the furnace.

One of example of the fluidized bed muddy wastage incineration apparatus will be described in detail with reference to FIG. 3, hereinafter.

An incineration furnace 1 includes a perforated plate 2 and an air chamber 3 in the lower portion thereof, while the dehydrated mud, which contains pulverized coal or fine granular coal. is supplied from the top portion of the incineration furnace 1 therein from a mud supply device 4. The air which is required for fluidizing and combustion is supplied through a blower 8, damper l5 and duct 9 to the air chamber 3, thereby fluidizing by passing through the perforated plate 2 the fluidizing medium particles such as cement clinker and the like as well as the mud which contains pulverized coal and fine granular coal, said particles and mud being positioned on the perforated plate 2, and thus the fluidized bed is provided. The operation of the incineration furnace begins with heating the fluidized bed by using a burner 6a. after which the incineration of the wastage proceeds due to the combustion of the pulverized coal (or fine granular coal) mixed with the muddy wastage. If the heat accruing from the combustion of the pulverized coal is insufficient. a burner 6a is used as an auxili ary means. The waste gas is discharged through a duct 7 out of the furnace.

When the increase in the quantity of fluidizing gas is required for forming a fluidized bed 5. the waste gas is introduced from duct 7. to thereby supply the waste gas through a damper l4 and blower 16 into the duct 9.

For operation of the incineration furnace 1, it is required to control the quantity of air and waste gas to be mixed therewith. To this end, a signal 11 which represents the supplied amount of muddy wastage and is obtained in connection to R.P.M. of a rotary feeder of the muddy wastage supply device 4, and a temperature. signal 18 from a thermometer 1 adapted to measure temperatures at the fluidized bed 5, are fed into a control box 10, whereby inlet dampers l5 and 14 of the blowers 8 and 16 are each controlled by means of signals 12a and 12b, while the control valves l9a and 19b for controlling the amount of oil for burners 6a and 6b are controlled by means of signals 13a and BI). The burner 6a is primarily used for starting a furnace or for an auxiliary purpose, while the burner 6b is used for supplying combustible materials abundant in carbon content, such as heavy oil, to the fluidized bed 5 and is normally used in case the muddy wastage to be charged in the furnace 1 contains no pulverized coal or the like. On the other hand, a damper 22 provided in the secondary air supply duct 21 is controlled by means of a signal 20.

As is apparent from the foregoing description, the features of the present invention reside in that, for in cineration of combustible industrial wastage containing organic nitrogen, particularly muddy industrial wastage of a high water content; there is used a fluidizing bed which permits the incineration at an extremely low excessive air ratio (1.1 to L3); carbon components of no less than 20% by weight, based on the weight of the wastage, are mixed with the solid matter such as muddy wastage to thereby form a reductive atmosphere within the fluidized bed 5, while the temperature at the fluidized bed 5 is maintained to be not less than 500C to incinerate the wastage; nitrogen oxides produced are reduced by CO, H CH and the like which are thus produced; whereby nitrogen oxides may be removed from the waste combustion gas from the wastage in the form of nitrogen gas. According to another aspect of the invention, there are used, as fluidizing-medium, cement clinker particles containing a great amount of Fe O C50 MnO, A1 0 chrominum ore particles and manganese ore particles for the purpose of accelerating the aforesaid reductive reaction, thereby effectively reducing and removing nitrogen oxides.

The reactions which take place within the fluidized bed incineration furnace according to the present invention are summerized as follows: The following reactions take place for the combustible matter and the added carbon components, within the reductive fluidized bed which is maintained at a temperature of not less than 500C:

wherein C H represents hydrocarbon groups contained in the combustible matters, part of which is subjected to dry destillation and decomposition within the fluidized bed under a reductive atmosphere to thereby produce methane (CH and the like.

CO. H CH, which are produced from the aforesaid reactions maintain the fluidized bed in a reductive atmosphere, whereby nitrogen oxides produced simultaneously with the production of the aforesaid gases are reduced according to the following reactions:

2N0 +CO N CO:

N 0 CO N CO 2N0 2H N 2H O CH 4N0; 4N0 CO ZH- O CH 4N0 2N CO ZH O The quantity of CO produced within the fluidizing bed according to the above reactions in much great as compared with that of nitrogen oxide, such that excessive CO, H C H CH and the like are oxidized by means of the secondary air in a space over the upper surface of the fluidized bed to be converted into CO and H 0 to present harmless gases.

When incinerating sewage mud having a water content of 78%, solid matter of 22% and nitrogen content in solid matter, of 5.5%. by using the above fluidized bed incineration furnace, the concentrations of nitrogen oxides (NO,) in the waste gas are as follows:

when pulverized coal is added 65 ppm when pulverized coal is not added 1,230 ppm It will be understood that the above description is merely illustrative of preferred embodiments of the invention. Additional modifications and improvements utilizing the discoveries of the present invention can be readily anticipated by those skilled in the art from the present disclosure, and such modifications and improvements may fairly be presumed to be within the scope and purview of the invention as defined by the claims that follow.

What is claimed is:

1. In a method for incinerating combustible industrial wastage containing organic nitrogen compounds in a fluidized bed, wherein air for use in combustion is blown into a furnace from below to fluidized noncombustible fluidizing medium placed within said furnace. for forming a fluidized bed, and at the same time said combustible industrial wastage is supplied into said furnace from the upper portions thereof, which furnace has been preheated to a temperature above the combustion temperature of said combustible industrial wastage which is to be incinerated in said fluidizing bed, the improvements comprising the steps of: supplying combustible fuel material abundant in carbon content with said combustible industrial wastage into said fluidized bed; simultaneously maintaining the interior of said fluidized bed in a reductive atmosphere and at a temperature higher than the combustion temperature of said fuel material and the combustion temperature of said combustible industrial wastage; incinerating said combustible industrial wastage in the reductive atmosphere in said fluidized bed and producing nitrogen oxides from the combustion of the organic nitrogen compounds contained in said combustible industrial wastage and reducing the nitrogen oxides thus obtained from the organic nitrogen compounds within the reductive atmosphere of the fluidized bed and thereby removing the nitrogen oxides from the combustion gas produced by the combustion of said combustible industrial wastage and said fuel materials abundant in carbon content.

2. A method for incinerating industrial wastage as defined in claim 1, including the step of providing said flu idized medium particles as cement clinker particles. which contain Fe O Al O Cr O and MnO as cataylsts.

3. A method for incinerating industrial wastage as defined in claim 1, including the further step of providing said fluidized medium particles as chromium ore particles.

4. A method for incinerating industrial wastage as defined in claim 1, further including the step of providing said fluidized medium particles as manganese ore particles.

5. A method for incinerating industrial wastage as de fined in claim I, wherein the resultant combustion gases obtained from the prior steps are mixed with air and maintained at a temperature above the combustion temperature of the combustible gases and below l,000 C for completing the combustion of the combustible gases without producing nitrogen oxides from the nitrogen gas.

6. A method for incinerating industrial wastage as defined in claim 5, wherein the resultant gases from the previous steps are at least in part supplied with the air blown into the furnace to fluidize the non-combustible fluidizing medium placed within said furnace and further to control the oxygen content of the fluidizing gas.

7. A method for incinerating industrial wastage as defined in claim 1, including the further step of automatically controlling the quantity of combustible fuel material abundant in carbon content that is supplied to the fluidized bed and simultaneously automatically controlling the oxygen content of the fluidizing air blown into the furnace from below, in response to the flow of industrial wastage into the furnace and the temperature of the fluidized bed.

Claims (7)

1. IN A METHOD FOR INCINERATING COMBUSTIBLE INDUSTRIAL WASTAGE CONTAINING ORGANIC NITROGEN COMPOUNDS IN A FLUIDIZED BED, WHEREIN AIR FOR USE IN COMBUSTION IS BLOWN INTO A FURNACE FROM BELOW TO FLUIDIZED NON-CONBUSTIBLE FLUIDIZED MEDIUM PLACED WITHIN SAID FURNACE, FOR FORMING A FLUIDIZED BED, AND AT THE SAME TIME SAID COMBUSTIBLE INDUCTRIAL WASTAGE IS SUPPLIED INTO SAID FURNACE FROM THE UPPER PROTIONS THEREOF, WHICH FURNACE HAS BEEN PREHEATED TO A TEMPERATURE ABOVE THE COMBUSTION TEMPERATURE OF SAID COMBUSTIBLE INDUSTIAL WASTAGE WHICH IS TO BE INCINERATED IN SAID FLUIDIZING BED, THE IMPROVEMENTS COMPRISING THE STEPS OF SUPPLYING COMBUSTIBLE FUEL MATERIAL ABUNDANT IN CARBON CONTENT WITH SAID COMBUSTIBLE INDUSTRIAL WASTAGE INTO SAID FLUIDIZED BED; SIMULTANEOUSLY MAINTAINING THE INTERIOR OF SAID FLUIDIZED BED IN A REDUCTIVE ATMOSPHERE AND AT A TEMPERATUE HIGHER THAN THE COMBUSTION TEMPERATURE OF SAID FUEL MATERIAL AND THE COMBUSTION TEMPERATUE OF SAID COMBUSTIBLE INDUSTRIAL WASTAGE; INCINERATING SAID COMBUSTIBLE INDUSTRIAL WASTAGE IN THE REDUCTIVE ATMOSPHERE IN SAID FLUIDIZED BED AND PRODUCING NITROGEN OXIDES FROM THE COMBUSTION OF THE

2. A method for incinerating industrial wastage as defined in claim 1, including the step of providing said fluidized medium particles as cement clinker particles, which contain Fe2O3, Al2O3, Cr2O3 and MnO as cataylsts.

3. A method for incinerating industrial wastage as defined in claim 1, including the further step of providing said fluidized medium particles as chromium ore particles.

4. A method for incinerating industrial wastage as defined in claim 1, further including the step of providing said fluidized medium particles as manganese ore particles.

5. A method for incinerating industrial wastage as defined in claim 1, wherein the resultant combustion gases obtained from the prior steps are mixed with air and maintained at a temperature above the combustion temperature of the combustible gases and below 1,000* C for completing the combustion of the combustible gases without producing nitrogen oxides from the nitrogen gas.

6. A method for incinerating industrial wastage as defined in claim 5, wherein the resultant gases from the previous steps are at least in part supplied with the air blown into the furnace to fluidize the non-combustible fluidizing medium placed within said furnace and further to control the oxygen content of the fluidizing gas.

7. A method for incinerating industrial wastage as defined in claim 1, including the further step of automatically controlling the quantity of combustible fuel material abundant in carbon content that is supplied to the fluidized bed and simultaneously automatically controlling the oxygen content of the fluidizing air blown into the furnace from below, in response to the flow of industrial wastage into the furnace and the temperature of the fluidized bed.

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