WO1986007602A1

WO1986007602A1 - A powder additive for use in the combustion of solid materials, and the use of the powder additive

Info

Publication number: WO1986007602A1
Application number: PCT/DK1986/000064
Authority: WO
Inventors: Niels Knud Erik Jacobsen
Original assignee: Sparol International Aps
Priority date: 1985-06-20
Filing date: 1986-06-11
Publication date: 1986-12-31
Also published as: DK151194B; FI81375B; DK280385A; AU5963386A; FI870692A0; FI81375C; FI870692A; DK280385D0; DK151194C; EP0229090A1

Abstract

A powder additive containing dicalcium phosphate and ammonium chloride in combination with 0, 1 or several of the following further ingredients: perborate, a manganese compound, salpetre, iron vitriol, magnesium sulphate and calcium nitrate. The powder additive can be used to counteract the formation of deposits in furnace, boiler and filter, as well as for the reduction of environmental contaminating discharges during combustion of solid materials.

Description

Title: A Powder Additive for Use in the Combustion of Solid Materials, and the Use of the Powder Additive.

Technical Field

The present invention relates to a powder additive for use in the combustion of solid materials. The invention further relates to the use of the powder additive for counteracting the formation of deposits in furnaces, boilers and filters as well as reduction of environmental contaminating discharges during combustion.

Background Art

In connection with the combustion of solid materials, such as waste products, including plastics containing waste or garbage, coal, coke and straw and in crematories it is well-known to encounter a number of problems in the form of interruptions and stoppages of operation as well as incomplete combustion, leading to the formation of deposits, corrosion, discharge of environmental contaminating substances and reduction of efficiency.

A conventional combustion system or plant consists in principle of three main elements, viz. furnace, boiler and filter.

A satisfactory operation of the system requires a combustion, which is so complete that no interruptions of operation arise due to sediments and deposits in the individual parts or clogging of filters. It must furthermore be avoided that the operation has to be stopped on account of discharges exceeding the permissible limits.

Furnace.

The furnace part is in most cases provided with a refractory lining, which has to be kept intact and reasonably clean. At normal use deposits are deposited, which have to be removed intermittenly. The removal of such deposits has previously been very difficult, as hard-handed cleaning methods, such as pneumatic chiseling and shootings, must be applied; these methods will often result in damages to the refractory lining. Repair of the refractory lining is expensive, time consuming and difficult and may involve a sanitary risk to the repairer.

Boiler. The boiler part may be of different constructions, e.g. either with horizontal or with vertical tubes.

The problems are in principle identical in the various types of boilers, for which reason they are only explained in relation to boilers with vertical tubes; this should not be considered a limiting factor.

Deposits in boilers are usually formed quickly and to a great extent. The deposits reduce the heat transfer through the tube walls to the thermal medium and consequently reduce the efficiency of the boiler. When the deposits in the boiler have reached an unacceptable level, they should be removed to ensure a satisfactory operation of the system. The necessary removal of the deposits in boilers is the usual reason for interruptions in operation.

Removal of deposits in the boiler is work-consuming and expensive and more or less injurious to health.

An effective cleaning of all tubes is often impossible, as the deposits cannot be removed without damage to the tubes, i.a. on account of corrosion of the tubes. As a consequence, the boiler operates periodically with one or several tubes sealed until they can be replaced. This replacement is usually performed in connection with the annual repair normally taking place in the summer Besides, cleaning of boilers is normally so difficult that the cleaning has to be performed by skilled chimney sweepers, who normally use motorized brushes and often have to cut through clogged tubes by means of iron bars.

For removing particularly hard deposits supply of water to the hot boiler is also used to effect that the deposits are burst off in pieces. These pieces are difficult to remove, and the method further involves the risk of the boiler being damaged.

Filter.

It is often necessary to include a filter part to fulfil the present environmental requirements. The filter part serves to prevent discharge of particulate impurities, such as flyash, soot, loose deposits and other substances which would otherwise pass out into the atmosphere from the combustion system.

In the event of great amounts of particulate impurities problems may arise in connection with the filters. These problems have in practice resulted in the unacceptable but necessary consequence of disconnecting the filters to make the system operational.

Danish Patent Specification No. 147,407 discloses the use of dicalcium phosphate to reduce the thickness of surface deposits in oil-fired systems affected by exhaust gases. This process has, however, in practice turned out to result in a completely unsatisfactory effect.

Danish Patent Specification No. 140,343 describes a process of complete or partial neutralization of the acid combustion products formed by combustion of sulphurous fuel by continuous and simultaneous injection of the following compounds: alkali-metal nitrate, ammonium nitrate, magnesium carbonate, carbon and ammonium carbonate. It is stated that the ammonium carbonate ingredient is of considerable importance for the achievement of an efficient neutralization. The agent used by said process is particularly developed for use in oil-fired systems and is primarily intended to neutralize the acid products, especially sulphur dioxide, formed by the combustion of the sulphur. The above known agent is in practice dosed to the boiler. The addition presents corrosive problems in the boiler and does not prevent the formation of deposits.

It is known from Danish Patent Specification No. 143,183, which Is a patent of addition to Patent No. 140,343, to replace magnesium carbonate in the known agent completely or partially with calcium hydroxide. The presented reason for using calcium hydroxide together with the other components coming into consideration is that a more efficient acid neutralization is apparently obtained. It has, however, in practice turned out that this amended agent is encumbered with the same drawbacks as the agent according to the main patent.

Disclosure of the Invention

The object of the present invention is to remedy the drawbacks of the prior art stated above and is described In detail below.

The object of the Invention is obtained by providing a powder additive according to the invention which is characterised by the subject matter of the characterising clause of claim 1.

The inventive powder additive can advantageously be used in the way described in the characterising clause of claim 4. The powder additive according to the invention is characterised by containing the following ingredients:

1) dicalcium phosphate,

2) ammonium chloride (sal-ammoniac powder)

in combination with 0, 1 or several of the following further ingredients:

3) perborate, such as sodium perborate and potassium perborate,

4) a manganese compound, e.g. manganese salt such as manganese sulphate,

5) saltpetre, such as NaNO₃ and KNO₃,

6) iron vitriol (FeSO₄, 7H₂O),

7) magnesium sulphate (Epsom salts), and

8) calcium nitrate (Ca(NO₃)₂).

Other additives may of course be present if suitable for the intended use.

A mixture of the two compulsory ingredients as well as perborate may e.g. be used for the combustion of straw.

The optimum mixture by using the two compulsory ingredients as well as perborate is 75% by weight of dicalcium phosphate + 5% by weight of perborate and 20% by weight of ammonium chloride. In case of combustion of waste or garbage this mixture will normally be used in an amount of 100-150 g/ton of fired waste (industrial waste mixed with domestic garbage).

100 g/ton of fired straw is used in the combustion of straw.

The amount of additive must be increased if the waste is wet, which is often the case with straw. A mixture of dicalcium phosphate, sodium phosphate and ammonium chloride may e.g. be used for the combustion of coal and coke. The combustion of coal and coke is, however, improved considerably if manganese sulphate and calcium nitrate are also added to the additive. As a result of the use of this additive mixture for the combustion of coal and coke the furnace is kept clean, fewer clinkers and less flyash being formed.

The use of an additive mixture according to the invention for combustion in crematories may reduce discharge of toxic substances, such as dioxines. It is normally difficult to avoid toxic discharges of this type in connection with combustion tasks with frequent cold starts, which renders the achievement of sufficiently high temperatures for complete combustion of e.g. poisonous substances difficult.

The same applies to combustion of waste or garbage.

It is preferred in connection with the combustion of heavily polluting materials, such as plastic-containing waste or garbage, that the additive contains ingredients of each of the above eight types, this yielding the optimum ensurance against noxious discharges.

The various ingredients may be mixed in the following ratio:

1) dicalcium phosphate 45-93% by weight, preferably 75% by weight,

2) ammonium chloride 5-50% by weight, preferably 20% by weight,

3) perborate 0-20% by weight, preferably 5% by weight, 4) a manganese compound 0-10% by weight,

5) saltpetre 0-10% by weight,

6) iron vitriol 0-15% by weight, 7) magnesium sulphate 0- 8% by weight,

8) calcium nitrate 0-10% by weight.

75-300 g, preferably 100-150 g of additive of the chosen composition may be used for the combustion of 1000 kilogram of solid material.

The powder additive according to the invention has surprising advantages when used in combustion systems, such as systems for the combustion of

a) waste or garbage, including plastics containing waste, b) solid fuel, such as coal and coke, and c) straw d) as well as cremation.

The combustion is supported by the use of the powder additive according to the invention. As a result a new formation of deposits is counteracted and present toxic substances are burned to non-toxic combustion products. The powder additive further ensures a limitation of the formation of flyash, and the powder keeps the boiler dry and leads to a loosening of any deposit, which may already be present.

When using of the powder additive, the powder Is fed continuously Into the furnace in such a manner that the powder reaches the flames in the form of a mist. By adding the powder directly to the flames it gets into direct contact with the ingredients which would later result in deposits. The powder also gets into contact with the toxic ingredients which have to be removed before the exhaust gas is let out into the atmosphere. The powder additive ensures a complete combustion of the materials which would otherwise form deposits as well as of the toxic substances by converting them into non-toxic materials. A utilization of the calorific value of these substances is furthermore obtained by the removal of technically and sanitarily noxious substances.

A too high as well as a too low temperature in the combustion can result in the formation of deposits. Oxide scales may be formed if the combustion temperature is too high, and if the temperature is too low deposits are formed in the form of a moist mass containing toxic substances. Such deposits may be deposited in furnaces, boilers and filters. The Incomplete combustion at low combustion temperatures may moreover lead to discharge of toxic substances.

The inventive powder additive has a highly drying effect. A considerable reduction of the extent of deposits is obtained by means of the combined effect of a considerable improvement of the combustion and a reduction of the content of moist ingredients In the exhaust gas. These deposits are furthermore dried and loosened so that they are easily removed.

The following effects may be observed in the individual parts of the combustion system, when the inventive powder additive is added:

Furnace

A considerable reduction of the formation of deposits is effected in the furnace. In this manner a considerable reduction of the damages arising in the refractory lining during cleaning is obtained, and the cleaning can take place at greater intervals than previously. The cleaning may furthermore be performed quickly and convenientlywithout the previously mentioned sanitary risk to the cleaner. The cleaning of the furnace part after use of the additive according to the invention has thus been reduced to a quite small task, as there are no serious deposits to remove.

Boiler

The boiler part is kept completely dry and substantially free of deposits by using the inventive powder additive. The only deposits, which may occur, will be in the form of dry, easily removable deposits.

The toxic substances will be burned before the exhaust gas reaches the boiler part. The environment around the boiler Is thus improved drastically, the known inconveniences of smell being removed. This is a great advantage in the daily, work around the boiler and particulary In connection with the cleaning of the boiler.

The cleaning of the boiler can now be performed at longer intervals, and it has turned out that the cleaning has been made easy, and can without difficulties be performed by the persons normally operating the combustion system. It will consequently not be necessary to call a skilled chimney sweeper.

The amount of waste produced as a result of the cleaning of the boiler has been reduced drastically. A system which could function for two weeks between each cleaning of the boiler has previously been considered a well - functioning system. It has now surprisingly turned out that even systems, which have previously not functioned particularly good, will often be able to function for 7 or 8 weeks between each cleaning of the boiler by means of the inventive agent. The duration of the periods of operation has often been dictated by the requirements (varying from country to country) of the authorities for the environment, and from a technical and environmental point of view the systems will often be able to operate properly for even longer periods. The deposits formed are of a loose structure and easily removable. The previously criticizable process, in which the deposits are burst off by supply of water to the hot boiler, is consequently no longer of interest.

The additive according to the invention may of course be used as desooting agent, the main object is, however, to ensure a combustion of the solid fuel to such a complete extent that damaging deposits and environmental problems in the form of discharge of toxic and malodorous gases and particles to the surroundings are avoided.

The efficiency is increased considerably, the ingredients previously transformed to damaging waste now being part of the combustion and thus utilized for the production of energy.

A boiler increases of course the utilization of heat to a considerable extent, no insulating deposits preventing transfer of heat to the heat transferring medium (e.g. water) being present.

A considerable reduction of corrosion of the boiler is obtained by using the inventive additive, the complete combustion in the boiler involving that the boiler remains dry. Besides, a conveyed amount of powder additive may support this effect. Dolomite or magnesite has previously been added to coal to obtain a drying of the boiler. The effect of this addition was, however, so small that this process has now been abandoned. The cleaning of the boiler is now considerably more easy than previously. The boiler just has to be opened in the bottom, whereafter the loose deposits can be removed by exsuction. The boiler is further opened at the top to ensure that the tubes are clean. Should this as an exception not be the case, it is possible to remove the deposits, if any, in a simple manner by means of a brush. In boilers with horizonal tubes the Cleaning is naturally performed in a corresponding ma-nner from side to side.

Filter

By using the powder additive according to the invention the content of solid particles in the exhaust gas has been reduced to such a considerable extent that the filter will no longer be a limiting factor for the operation of the combustion system. This circumstance can be illustrated by an example from practical life in connection with a new straw furnace. The furnace could only function for 8 or 10 days before the need of a thorough cleaning performed by a chimney sweeper arose. The filters were moreover clogged even before, so that the system was completely inoperative after a short period, unless the filters were disconnected. By using the inventive additive the filters could be connected and the system was operative without the chimney sweeper being called. The system in question how operates for 8 weeks without cleaning.

The powder additive according to the invention presents considerable savings. The costs of the powder are thus only one fourth of the costs for the work to be performed by a skilled chimney sweeper. To this should be added the other far more important advantages obtained by using the inventive powder, such as a reduction of the damages to the system, better utilization of the calorific value of the burned material as well as an improvement of the environment.

The composition of the powder additive according to the invention varies with the material burned. Consequently it is advantageous to add dyestuff to the powder additive, in order to facilitate the distinction of the various types of utilization of the inventive powder additive from each other. The reaction mechanism causing the effects of the powder additive are not yet fully elucidated, but the obtained effect exceeds the additive effect of the individual components of the additive.

As a further example of the excellent effect obtained by the additive according to the invention may be mentioned:

An existing coal-burning district heating station faced problems as to the fulfilment of the environmental requirements.

100 g of additive consisting of 75% by weight of dicalcium phosphate, 5% by weight of sodium perborate, 15% by weight of ammonium chloride + 5% by weight of manganese sulphate per ton of coal resulted after three or four days use not only in fulfilment of the environmental, requirements since measurements showed that the pollution was only one fourth of the permissible.

The full effect was not reached in the first period after addition of the additive on account of loosening of de¬posits already present. After removal of these "old damages" the combustion was ideal.

Claims

Claims:

1. A powder additive for use in the combustion of solid materials, c h a r a c t e r i s e d by containing the following ingredients:

1) dicalcium phosphate,

2) ammonium chloride (sal-ammoniac powder)

in combination with 0, 1 or several of the following further ingredients:

3) perborate, such as sodium perborate and potassium perborate,

4) a manganese compound, e.g. manganese salt such as manganese sulphate,

5) salpetre, such as NaNO₃ and KNO₃,

6) iron vitriol (FeSO₄, 7H₂O), 7) magnesium sulphate (Epsom salts), and 8) calcium nitrate (Ca(NO₃)₂),

2. A powder additive as claimed in claim 2, c h a r a ct e r i s e d by containing the following ingredients:

1) dicalcium phosphate 2) ammonium chloride

3) perborate

in combination with 0, 1 or several of the following ingredients:

4) a manganese compound 5) salpetre

6) iron vitriol

7) magnesium sulphate

8) calcium nitrate.

3. An additive as claimed in claim 1, c h a r a c t e r i s e d by comprising the the following ingredients calculated as percentage by weight of the additive:

1) dicalcium phosphate 45-93% by weight, preferably 75% by weight,

2) ammonium chloride 5-50% by weight, preferably 20% by weight,

5) salpetre 0-10% by weight,

6) iron vitriol 0-15% by weight,

7) magnesium sulphate 0- 8% by weight,

8) calcium nitrate 0-10% by weight.

4. Use of a powder additive as claimed in claim 1 forcounteracting the formation of deposits in furnaces, boilers and filters, as well as reduction of noxious discharges during combustion.

5. The use as claimed in claim 4, c h a r a c ¬t e r i s e d in that the powder additive is introduced continuously in the form of a powder mist in the blazing zone of the furnace.

6. The use as claimed in claim 4 or 5, c h a r a c t e r i s e d by the addition of additive in such amounts that a drying effect is obtained in the furnace.

7. The use as claimed in claim 4, c h a r a c t e r i s e d in that 75 - 300 g of additive is used for 1000 kilogram of solid fuel.