EP0159987A1

EP0159987A1 - A method of preventing, self-ignition and dust-explosion when handling a powderous peat fuel

Info

Publication number: EP0159987A1
Application number: EP84900141A
Authority: EP
Inventors: Hakan Kinnerberg
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-12-13
Filing date: 1983-12-12
Publication date: 1985-11-06
Also published as: SE8207128D0; WO1984002346A1; SE8207128L; FI850115A0; FI850115L; SE436285B; NO843007L

Abstract

On élimine le risque d'une auto-inflammation ou d'une explosion de poussière lors de la manipulation d'un combustible de tourbe pulvérulent dont la teneur en eau est inférieure à 30 % en forçant les particules individuelles de tourbe à se lier entre elles afin de former des agglomérats relativement faibles et ne donnant pas de poussière en mélangeant aux particules une substance liquide ou pulvérulente dont le poids représente au plus 20 % du poids de la poudre sèche. La substance peut comprendre un produit du pétrole ou une huile végétale, ou alors une substance pulvérisée qui fond lorsqu'elle est chauffée, par exemple du sucre ou de la paraffine.The risk of self-ignition or dust explosion is eliminated when handling a powdery peat fuel with a water content of less than 30% by forcing the individual peat particles to bond together in order to form relatively weak and dust-free agglomerates by mixing with the particles a liquid or pulverulent substance whose weight represents at most 20% of the weight of the dry powder. The substance may include a petroleum or vegetable oil product, or a pulverized substance which melts when heated, for example sugar or paraffin.

Description

A method of preventing, self-ignition and dust-explosion when handling a powderous peat fuel

Field of invention

Dry peat is a combustible substance, which readily oxidizes and which gives off, inter alia, combustible gases.

There is also a risk of explosion, when clouds of fine peat particles are created and ignited. The lower

3 explosion risk lies at 45-60 grams per m .

The risk of self-ignition and^' dust-explosion increases with a fall in moisture content and with a decrease in particle size. The greater the specific surface area, i.e. the area in contact with the ambient, oxygen-rich atmosphere, the greater the risk of explosion. Raw peat found in a peat bog consists of from 90 to 95% water. This water content can be lowered to 80-85% by draining the bog, through ditches. By taking up the peat, processing the same and allowing it to dry in sun and wind, it is possible to reduce the water content thereof from 35 to 50%. Lump peat/machine peat and milled peat having moisture contents of from 35-50% are today used as fuels. Particularly low moisture contents can be obtained, by thermally drying the peat in special drying apparatus herefor. Pulvurent peat having a water content of 30% and below is comminuted in the drying process into extremely fine particles, which means that the risk of self-ignition and dust explosions is particularly high. Consequently, peat powder is today produced either for direct combustion, or for the manufacture of pellets and briquettes. A decrease in the risk of explosion opens new fields of use, thereby to enable the powder to be produced in a separate plant or mill, and then handled, i.e. transported, stored and burned in powder-fuel systems. Prior art methods

Various methods have earlier been proposed for processing peat in order, among other things, to facilitate the handling thereof. The majority of the known methods relate to the manufacture of briquettes and the like for combustion purposes, and examples of such methods are found in US-A-1 ,546,785 (Illemann) and DE-B-972,171 (Zdralek) .

For example, there is described in DE-B-972,171 (Zdralek) a method of converting raw peat into a coal-like product, by finely dividing the peat and adding an electro¬ lyte and other coagulents.

In DE-B-22 54 150 (Sebreg) there is described a method of manufacturing fibre-granulates from natural or synthetic, non-moisturized fibres in the form of fibre aggregates of low coherence, by applying to the upper surface of the aggregate a liquid, such as to form liquid menisci between overlying fibres, these menisci, when vapourizing or evaporating the liquid, increasing the coherence between the fibres.

SE-B-45,474 (Torfoleum GmbH) describes a method of producing a building material from sludge or peat, by adding thereto chlorides of multivalent metals.

None of these publications, describing known methods, deal with the aforementioned problem, namely that of eliminating the risk of self-ignition and dust-explosions when handling powderous peat fuels.

SU-A-28620 D/16 (Belo Peat Inst) describes a method for determining the risk of self-ignition of a powdered peat, in which a peat sample is heated under anaerobic conditions to 900 C, whereafter observations are made on the heated sample. The accuracy of the method can be improved, by treating the powdered peat with a mixture of different acids, at a temperature of from 80 to 90°C. This method solely provides a calculation of the risk of self- ignition of the peat, subsequent to having been stored for different lengths of time. No suggestion is made, however, to solving the problem of avoiding self- ignition and dust-explosions.

Further, according to available prior art petroleum products such as oil have been added to peat, coal and other combustibles with i.e. the following aims:

1 ) To facilitate dewatering of raw peat the peat may initially be treated with different acid or basic minerals. By thereafter adding oil or tar which is absorbed . in the peat water is expelled. Non-dewatered peat comprising non-desintegrated particles is handled (SE-B-110 ,996

(Engel et al) ) .

Also other substances than oil may be added to raw peat to facilitate subsequent treatment such as briquette manufacturing, cf. SE-B-59,991 (Gesellschaft fur maschinelle

Druckentwesserung) and SE-B-103,674 (Separator).

2) More heavy oils and tar can be used as a binding agent at briquette manuf cturing from for instance peat, cf. DE-B-103,509 (de Faucheux d'Humy) . It is then compulsory to use an oil or tar which does not solidify at cooling.

Each briquette comprises a fixed mass in which the original particles are fixedly joined to each other.

A similar briquette manufacturing process is described in UK-B-352,542 (Rudeman) . In both cases the oil or tar serves as an agent which in cold state has shaping and binding capacity.

3) Combustibles having a low content of volatile components are often difficult to ignite which may create problems at combustion. By adding oil, preferably a lighter oil such as Diesel oil or kerosene the amount of volatile components is increased and the ignition characteristics are improved. DE-B-27 11 082 (Shell) describes an example thereof.

4) When handling briquettes, pellets etcetera dust may loosen from the surface thereof. The briquettes may then be treated with oil as proposed in DE-B-301,138

OMPI _ (Stechele) . Then the dust will be bound to the surface which is, thus,encased by an oil layer. Then, however, there is no treatment of the inner particles of the briquettes. GB-B-842,711 (Simon-Carves) describes a process in which a coal-powder-dust is treated with oil and formed into an "aggregated body". Large pieces of baked coal powder are obtained. This means that treatment of these "aggregated bodies" is not similar to treating a fine powder with appertaining risks for self-ignition.

Object of invention

An object of the invention is to provide a method of preventing self-ignition and dust-explosion when handling a powderous peat fuel having a water content of beneath 30% which method is cheap and easy to practise and avoids the shortcomings of previous methods.

Summary of the invention A method according to the invention which fulfils this object is characterized by admixing with the peat powder a liquid or powderous substance whose weight constitutes at most 20% of the weight of the powder, said substance acting upon the individual particles in a manner to cause them to bind together by flocculation to form relatively weak non-dusting agglomerates.

The additive substance is mixed uniformly throughout the whole of the powdered peat mass. The substance can be in liquid or powder form. When the additive is in liquid form, the amount used shall be so small that the mixture of peat powder and said substance is still powderous. In this respect, the amount of additive used shall be limited to at most 20% by weight, as beforementioned, and can be considerably less. When the additive is in liquid form, it suitably comprises an oil, such as a petroleum product or a

OMPI vegetable oil.

The substance may also be volatile, and may, for example, be Diesel oil.

When the additive substance is a powder, it preferably comprises a substance which melts when subjected to limited heat, such as sugar or paraffin. Oils wet peat better than does water, because - among other things - the chemical structure of the oil is more similar to that of peat than is the chemical structure of water. Thus, oil and peat both consist of long chains of carbon, hydrogen and oxygen atoms, the form and equilibrium state of which are favourable in achieving the effect desired. The peat particles are readily encased in a film of oil, and minute peat-dust particles readily adhere to the oil-film surfaces, and are also enclosed in the oil, where they are firmly bound.

A readily meltable powderous substance, such as sugar or paraffin, has similar properties, and is therefore suitable for use in the present context.

Laboratory tests have shown that an addition of 2-10% by weight of oil waste, Diesel oil (fuel oil 1) or paraffin, is sufficient to prevent the formation of dust and to form an oil skin which encloses the major part of even the smallest of the peat particles.

The effect sought for increases with increased quantities of additive, up to a certain limit, at which no furthe^'r improvement can be observed.

With regard to the lowest limit, tests have shown that an additive amount as low as 2% by weight will afford an effect. It is probable, however, that an acceptable effect can be obtained with certain substances in amounts of, for example, 1% or thereabout.

With regard to the.-upper 1-imit further tests have shown that at least when admixing a volatile petroleum

OMPI product such as light fuel oil or diesel oil to much thereof will lead to difficulites when-it comes to still treating the peat as a powder. Therefore, a maximum would in this case be about 6% by weight of the powder. An oil content of 3 a 4 % by weight is preferred as being an optimum presenting full safety and still very good powder treatment characteristics. Examples

Tests have been carried out on dried fuel peat having a moisture content of about 20%. The peat was reduced to powder form.

The powder readily gave rise to clouds of dust, when agitated or disturbed.

Tests were made using three different petroleum products, namely waste oil (0), Diesel oil, Eo1 (D) , and paraffin (F) , together with a vegetable oil, maize oil (M) .

The substances were admixed with 50 grams of powder, whereafter the powder was agitated vigorously. The substances were mixed with the powder, and the fact whether dusting tendencies decreased or stopped was registered. The consistency of the peat powder was observed.

OMPI o The following table relating to the tests made was compiled.

Test Additive Additive Observation Result

No. grams % by wesight

01 0.5 1 The oil coagulates Dusts Difficult to mix The lumps disappear when worked vigorously

02 2.5 5 Dusts

02 5 10 Dusts slightly

04 10 20 Does not dust

D1 0.5 1 - Diesel oil is Dusts rapidly absorbed slightly and mixes readily with the powder No lumps

D2 2.5 5 Does not dust

D3 10 _"— Does not dust

D4 10 20 Does not dust D5 2.5 2. 5 -"- Does not

(100 gr. powder) dust

F1 0.5 1 The paraffin is Dusts rapidly absorbed slightly and mixes readily with the powder No lumps

F2 2.5 5 Does not dust

F3 10 —" — Does not dust F4 10 20 __!!__ Does not dust

M1 2.5 The oil coagulates Dusts Difficult to mix The lumps disappear when worked vigorously

M2 10 Dusts slightly

M3 10 20 Does not dust

OMPI Remarks: The tendency of the peat powder to remain in the vessels and funnels used increased with increasing amounts of additive. The powder was not sticky, however. A similar effect is to be expected if a heavy fuel oil is used instead, although in this case a certain amount of heat must be applied.

A corresponding result is to be expected when admixing the peat powder with a substance which melts readily when a low heat is applied, such as sugar or paraffin for example.

When the additive substance is in powder form, it is necessary to apply sufficient heat to bring said substance into a form in which the finely-divided peat particles can be encased. As will be understood, it is also conceivable to use powderous substances which are not readily melted. Such substances require more heat and thus increase costs, and are therefore of less interest in respect of the present invention.

It is also possible, within the scope of the inven- tion, to add one or more additives which stabilize the obtained effect. An example of such a stabilizer is one which prevents the oil from evaporating.

In the present specification a "powder" refers to discrete particles of a dry substance which are smaller than 100 jum. The term "dust" as used in the expression "dust-explosions" refers to a particulate, combustible substance which may be air-borne and normally has a particle size smaller than 500 jum.

Industrial applicability

From the above follows that preparation of the peat powder according to the invention accomplishes the following special advantages:

- increased adhering forces between the particles; - relatively weak agglomerates are obtained in which the particles are not fixedly joined to each other;

OMPI the powder particles are movable relative to each other, and the powder may therefore still be treated as a powder; and the increased adhering forces and the weak, non-fixed agglomerates will bind the small dust particles within the powder which, thus, turns to be non-dusting.

These special characteristics make it possible to accomplish the overlapping goal with the new method, namely to avoid self-ignition and dust-explosions when handling a powderous peat-fuel of the kind under concern.

" EJ Ϊ

OMPI

Claims

1. A method of preventing self-ignition and dust- explosion when handling a powderous peat fuel which by drying is broken up into very fine particles having a water content of beneath 30%, characterized by admixing with the peat powder a liquid or powderous substance whose weight constitutes at most 20% of the weight of the powder, said substance acting upon the individual particles in a manner to cause them to bind together by flocculation to form relatively weak non-dusting agglome- rates.

2. A method according to Claim 1, characterized by admixing a petroleum product or a vegetable oil.

3. A method according to Claim 2, characterized by admixing a volatile petroleum product, such as a light fuel oil, Diesel oil, or paraffin.

4. A method according to Claim 1, characterized by admixing a powderous substance which melts when limited heat is applied thereto, such as sugar or paraffin.

5. A method according to claim 3, characterized by admixing an amount volatile petroleum product of between 2 and 6 % of the weight of the powder, preferably 3 a 4%,