Background of the Invention

1. Field of the Invention

The invention is a procedure for the manufacture of briquettes or pills for stoking made of stems from grain or straw or similar cellulo- siσ waste material with the admixture of a binding agent during com¬ pression, principally by trace or piston pression, at a pressure tempo¬ rarily raising the temperature in the straw briquette to an area be¬ tween 75 ^* C and 200 ^* C.

2. Description of the Prior Art

Such procedures are known, e.g. from DK-patent specification 148. 119 describing a procedure for the manufacture of compressed straw bri- quettes for stoking, which is peculiar in that for its binding agent it uses hydrous sludge containing organic material, notably sludge from sewage purification or biological gas recovery. The advantages stated for this invention is especially the removal of sludge by means of straw briquettes and the exploitation of the calorific value of the or- ganic content of the sludge, while the structure or deformation resi¬ stance of the briquette appear to be of less importance. Not surpri¬ singly, such briquettes have proved unsuitable for transport because they lack deformation resistance properties. The briquettes frequently crumble at the smallest physical degree of stress, e.g. when stored in piles.

From DK patent application 90/84 it is known that a binding agent can be used for the stabilisation of the deformation resistance of the briquette for the purpose of transport over relatively long distances. According to the latter application the binding agent is made uip of fly ash, which, compared with other known binding agents, is cheap

waste substance, which can even absorb a slightly increased moisture content in the straw. The drawbacks in using fly ash include the fact that the mineral content of fly ash involves a heavy mechanical wear on plungers and other parts in the manufacturing process and that the σon- tent of waste matter of the fly ash is not controllable with a view to substances polluting the environment. This, again, makes it inadvisable to use the ashes for fertilization.

From DK patent application 4471/81 we know of fuiel briquettes or pills, which as binding agent uses the substance of tallbek in an amount corresponding to 1 - 10 weight per cent. According to the ap¬ plication this binding agent shouild cause the effect that the briquet¬ te burns with a flame. Again, the drawback in this binding agent is that tallbek fails to ensure deformation resistance in the briquette sufficient enough to let the briquettes travel over long distances. As tallbek is an oily product with a content of high fatty acids, resinous acids, esters an unsaponifialble substances, this matter does not cor¬ relate very well with the press during the manufacture of the briquet¬ tes or the pills, since tallbek, which only becomes thin at 80 ^* C to 90 ^* C, glues together during coling and deposits in the matrix and in the cooling stretch. Finally, it shouild be stated that allbek is a material which has to be bought, which will often put a strain on a na¬ tion's balance of payments.

It is furthermore a known practice to use lignosuphonate under the trade name WAFOLIN as a binding agent, this substance produces poorly coherent briquettes, which easily crumble. Moreover, lignosulphonate has a sulphur content of abt. 5 per cent so the use of lignosulphonate will result in an increased emission of sulphur.

A commom feature of the known binding agents is that they all re¬ quire a hydrous contnet between 12 and 16 per cent in the straw, i.e. very dry straw. Under north-european climatic conditions drying to such a low hydrous contnet is seldom possible in the field before collecting the straw, and it has indeed turned ouiit that most of the straw uised for pressing briquettes has to be dehydrated before being uised for briquettes. This dehydration process in itself is energy-consuming and compoaratively cost demanding so as to lower the totals energy output

of straw.

It is the object of the present invention to provide a procedure for the manufacture of briquettes or pills made of straw or similar cellulosic waste material with a hydrous content even greater than 16 per cent using a binding agent to ensure a briquette of structural sta¬ bility which will sustain transportation over long distances, and that this binding agent shall not have inherent secondary effects in the form of e.g. increased wear on plunger or matrix, neither should it contain environmental pollutants. Furthermore, together with the fuel, the binding agent must be capable of going into a cycle in agiculture, in which e.g. the ashes from the incineration can be used as a supple¬ mentary fertilizer.

Summary of the Invention

According to the invention this object is achieved by admixing straw and similar waste material from pulses and protein plants to be used as binding agent. Straw from pulses and protein plants has a pro- tein-content between 30 and 40 g/kg« This protein is utilized during compression at high temperature together with the hydrous contents in the straw thus producing a coagulation of the proteins, which thereby bind the straw briquettes to a briquette of stable form having a rela¬ tively large resistance to physical stress. The most important feature of the specified binding agent is partly that it is possible to use straw with a hydrous content up to 75 per cent higher than previously without causing any deterioration of quality in the produced briquette, partly that it does not involve any abnormal wear on the plunger or the matrix. Besides, in its coagulated state, the binding agent acts as a lubricant between the straw and the matrix.

The residue from burning the straw briquettes is ashes which do not contain environmental pollutants, e.g. in the form af heavy metals, as all matters which are used for the manufacture of the straw briquet¬ tes may be found among the surplus production of an ordinary farm. This makes it only natural to use the ashes for fertilizing, from which it

can be seen that a cycle is provided for the constituents of the bri¬ quettes.

It has proved particularly appropriate to use straw from the pro¬ duction of peas and lupines as binding agent. In so doing, the rela- tively large amount of pulses' straw stemming from the growing of legu¬

_* minous plants is also turned to account. In frequently grown sorts the raw protein content is between 30 and 40 g/kg straw. For the binding agent to work effectively, it must be addes in an amount of up to 10 per cent, mainly 5 per cent. A particularly surprising effect of the procedure according to the invention is that the hydrous content of the straw is allowed to vary from 16 to 30 per cent, which has so far been prohibitive to the com¬ pression of straw briquettes. This is owing to the fact that when moist straw is being compressed into briquettes steam pockets arise which will impair the briquettes and produce poor cohesion. The effect of the larger hydrous content is probably explicable by the hydrous content of the straw in connection with the protein content of the binding agent . creating a stable bojid.

Detailed Description of the Preferred Embodiment

The following example is quoted to illuminate the invention; Straw having a hydrouis content of 24 per cent was finely cut in a shredding machine of the FARMHAND type to a cut size between 1 and 3 cm. In a mixing chamber comminuted pea straw is admixed after which the mixture is conducted to an eccentric press of the C.F. Nielsen brand, this press having proved adequately sturdy for the compression of straw briquettes. The action and operating conditions of such a press are well-known and so any description has been left out. The compressed briquettes are ejected from the press in one continuous string at a temperature of abt. 70 ^* C and are conducted along a cooling stretch to the stockyard, where the briquettes break off by free fall.

The produced straw briquettes have a dry solid content of abt. 92 per cent with a caloriferic value of around 4310 kcal/kg or 18045

kJ/kg. The stated values are very uncertain, dependent heavily as they do on the time of the year, climate, sort and constituion of the soil.