NO330295B1 - Method of manufacture of firing product - Google Patents

Abstract

A method of manufacturing a firing product wherein particles of sewage sludge and peat particles are compressed to form pellets or briquettes. The sewage sludge is dried to a solids content of 60-90% and ground. A long-fiber peat is used which is dried down to a solids value of 60-90%, preferably 12-15%, and ground to a particle size in the range of 0.2 to 10mm. A particle mixture is made with about 20 - 60 weight percent peat and 40 - 80 weight percent sewage sludge particles, which are extruded to compress the particles. Prior to the extrusion, the mixture can be added to water vapor to control temperature and humidity.

Description

Procedure for the production of fuel product, as well as fuel product

The invention relates to a method for the production of a heating product, as stated in the introduction to patent claim 1. It relates to a method for the production of a heating product where particles of sewage sludge and particles of peat are pressed together to form agglomerates, in the form of granules, pellets or briquettes ,

This combustion product has the character of an agglomerate, that is, a unit pressed together by particles, such as granules, pellets and briquettes. In what follows, the term "pellets" will be used.

Background

Sewage sludge is a problem material for most sewage systems. Due to the content of harmful substances, such as heavy metals, a problem has gradually arisen with using sewage sludge for fertilizer and soil conditioner or in open landfills. This in turn has led to the need for other ways to make use of the values contained in the sewage sludge. Many attempts have been made to find practical uses for sewage sludge as an energy source.

From US patent 4,225,457 (Schulz) it is known to use sewage sludge as a binder when pressing briquettes of shredded solid waste.

From US patent 5,797,972 (Schulz) it is known to make mechanically stable fuel briquettes with sewage sludge as the main ingredient, with the addition of coal and lime as binder.

From US patent 4,395,265 (Reilly et al 1983) it is mentioned that dried, ground sewage sludge is added to peat particles to bind the peat particles themselves into pellets for firing. This is not known to have resulted in a usable product, although it is open to pulverizing the end result and blowing it into a combustion chamber.

From US patent 5,389,114 (Forder 1995) it is known to mix 77% sewage sludge, 12.5% peat and 12.5% sawdust as raw material for fuel pellets. The manufacturing process includes several phases of mechanical and chemical treatment, and disinfection with microwaves. This procedure is complicated and requires the use of chemical additives.

From US patent 5,972,058 (Turkkeli, 1999) it is known to use granulated peat as an additive in a process where particles are manufactured from sewage sludge. This process requires that the sewage sludge is extruded in such a way together with the peat particles, that the cell structure in the sewage sludge is opened and the peat particles absorb. It is further assumed that the particles are coated with a coating material and further that they are hardened to provide sufficient stability.

From Korean patent application 200302906 (Ook 2003) it is known to press peat particles, sewage sludge and zeolite in a ratio of 65:25:10. This method therefore requires an additional additive.

From Swedish patent 524283 (Lindahl, 2002) it is known to press briquettes or the like from peat particles and sewage sludge, followed by an impregnation of the briquettes with paraffin, wax or a similar oily treatment agent.

From PCT publication WO 00/71477, a procedure for pre-treatment, pelletizing and drying industrial sludge for reuse is known. Sewage sludge and industrial sludge are two different basic materials, both in terms of content and properties. Here, the starting point is that the sludge has a high water content and that it must be drained. As a means of making the sludge pelletizable, a "dry substance", particularly organic waste, is added. After pelletizing, a final drying is carried out.

From D2, US patent document 5,797,972, it is known to dry sewage sludge before adding a binder and pelletizing. This gives no instruction on the addition of other materials and therefore no instruction on a procedure that is suitable for producing the mixed product that is stated to be known in the introduction to patent claim 1.

From Swedish patent document 522 179 it is known to add peat to sewage sludge, but this takes place according to the central example 5 by mixing "dry tanked" biosludge with a dry matter content of 29% with dried peat.

This last procedure corresponds to what is stated as prior art.

None of the known procedures have been satisfactory with regard to the most important parameters of production costs and product quality. With regard to manufacturing costs, the known methods have either required complicated equipment and/or a lengthy process. As regards the requirements for product quality, these have been met through the expensive use of additives and special steps in the manufacturing process.

Purpose

The main purpose of the invention is to come up with a manufacturing method which makes it possible to convert sewage sludge into an agglomerate, i.e. granules, pellets or briquettes, with satisfactory storage and transport properties, and which allows efficient and environmentally satisfactory combustion in various ovens.

There is a desire to create pellets or other compressions of particles, which provide sufficient transport and storage strength. This should be achieved without the use of additives.

It is also an aim to create a combustion product which allows any residues of heavy metals in the sewage sludge to be collected and treated in a satisfactory manner.

It is also desirable to obtain a heating product with good calorific values and complete combustion, with acceptable emissions of so-called "greenhouse gases".

The invention

The invention is described in patent claims. The procedure is characterized by the fact that

a) the sewage sludge is dried to a dry matter content of 60 to 90 percent by weight and ground,

b) that a long-fibred peat is used which is dried down to a dry matter value of 60-90

percent by weight, preferably 85 - 88 percent by weight and ground in a grinder to one

particle size in the range 0.2 to 10 mm,

c) that a particle mixture is made with approximately 20 - 60% by weight of peat and 40 - 80% by weight of sewage sludge particles in a mixing drum, and

d) that the particle mixture is extruded to compress the particles.

It has been shown that this procedure requires simple equipment and is easy to

implement. A good binding of the briquettes is achieved and firmness and transport and storage properties are also satisfactory. Moreover, the addition of expensive impregnation or strength-increasing additives is not required.

Patent claims 2-6 indicate particularly advantageous details of the invention. The heating product has been shown to have good handling and transport properties and satisfactory firmness and burning qualities.

The invention makes it possible to produce a heating product that is more affordable and better in relation to costs than comparable known heating products.

Example

An example of a method and a heating product is described below, where the method is illustrated in the drawings, as Figure 1 shows a flow chart for an example of a manufacturing process in accordance with the invention, while Figure 2 schematically shows a plant for carrying out the method in accordance with the invention

In Figure 1, the individual steps in an embodiment of the process in accordance with the invention are shown schematically in a flow diagram.

Peat, especially long-fibre grass turf, was extracted by plowing with known equipment. The peat was then placed in cones for drainage before being pressed and then ground in a grinder. When painting, other organic components can alternatively be added, such as sawdust, bark or fibrous agricultural waste with a certain dry matter content, possibly also livestock excrement.

The sewage sludge was received after dewatering. It was then centrifuged to approx. 20% solids content and added to a closed chamber for storage without degassing to air.

The sewage sludge was then ground in a grinder and, together with the peat particles, it was dried in a drum with heat input. Here it came out with a temperature of 60 - 70 degrees C. The mixed particle mass was then taken to hammering, where it came out with a temperature of 30 - 40 degrees C. Before the pellet machine, a silo was used to be able to temporarily store the mass, for thus being able to add the right amount to the pelletizing machine. Therefore, it also had to be possible to add steam to the mass before it is pelletised. So that you have an optimal temperature of 30 - 40 degrees C and 60 - 90% dry matter, preferably 85 - 88% dry matter.

Figure 2 shows the elements of a production plant based on receiving peat blocks and sewage sludge in bulk.

The starting point for the process and product in accordance with the invention is sewage sludge. In the example, sewage sludge extracted from a public treatment plant that receives sewage from homes was used. This sewage sludge was thus previously dewatered to increase the dry matter content.

The facility comprised a mechanical press 11 driven by a motor 12 and with a

intake opening 13 for peat blocks. This was not absolutely necessary to use if the pre-drying was good enough.

From the press 11, the peat mass is fed through a screw conveyor 14 with motor 15 which can remove additional water from the peat mass.

The peat mass is then fed to a grinder 16 which is driven by a motor 17 and which tears up the peat mass into particles.

The sewage sludge supplied to the facility is deposited in a closed chamber 18, to prevent gas, infectious substances and odors from being emitted from the sludge mass. The gas developed in the chamber 18 will be unpleasant. It can be pumped out with a pump 19, and burned in the oven until dry.

The invention requires a certain consistency and moisture content of the particles to be compressed. Therefore, the sewage sludge is centrifuged beforehand. The figure shows a mechanical press 20 in readiness should it be necessary.

In press 20, the dry matter content was increased to 20-30%.

To prepare the sewage sludge for mixing with the peat particles, it is taken from the press 20 to a grinder 22 driven by a motor 23. The grinder 22 can, for example, be adapted for operation with a tractor, for grinding biomass.

The peat particles from the grinder 16 and the sludge particles from the grinder 22 are transferred to a drum dryer 24, for example with screw conveyors or chutes not shown.

The drum dryer 24 is driven by a motor 25 and heats the particles to a temperature that is suitable for the further processing as will be described below. A drum furnace is used here, which is powered by its own fuel.

As pre-treatment for pelletisation, the mixture of particles is hammered in a hammer mill 26 driven by a motor 27.1 hammer mill the particles are crushed and have a temperature of 30-40 degrees before they are fed to a pellet machine 28 driven by a motor 29. From the pellet machine 28 they are finished pellets 30.send over a shaking table 31 to remove dust. They are then stored in a container 32. From there, the pellet mass can be transferred in loads or by pipe transport to a combustion plant.

In order to adjust the temperature and humidity in the mass supplied for pelleting, it is an advantage if water vapor is supplied from a steam boiler 33 or another steam generator at the inlet to the pellet machine 28, which may for example be a screw pelletizer. Steam can be used without overheating.

All motors and drive devices in this plant are included in a control system that allows control of the process so that it can be carried out continuously, with adaptation to varying pulp qualities, temperatures and other conditions that require adaptation of the process.

In the pelletizing equipment 28, a fusion of the particles takes place, starting from the lignin content found in the peat particles. This provides both bonding and hardening of the surface. Pellets manufactured according to the method in accordance with the invention acquire a consistency and hardness that allows blowing and suction through pipes and transport in bulk and also storage under controlled humidity conditions.

It has been shown that heavy metals that may be present in the sewage sludge remain in the ash residue after combustion. This makes disposal easier and prevents the spread of heavy metals in nature, which has occurred when sewage sludge is used as fertilizer or soil conditioner.

A particularly favorable composition of components is 30-50 percent by weight peat and 50-70 percent by weight sewage sludge, in both cases based on pre-dried mass, as described above. But this composition can vary in the range of 20 to 60 weight percent peat and 40 to 80 weight percent sewage sludge. This balance will depend on the fat content in the sewage sludge and the lignin content in the peat mass. In addition, it is controlled by the desired burning properties of the finished heating product.

Pellets made with approx. 30 weight percent peat and approx. 70% by weight of sewage sludge, was measured in a standardized "Ligno-test" equipment. Tests showed that approx. 98.7% of the pellets were undisturbed by the test impact. Based on the available results, it is assumed that this composition is particularly beneficial.

The pellet mass had a bulk density of approx. 0.85 kg/litre. This proved to be beneficial for the combustion, as it produced complete combustion, with no unburnt residues in the ash.

The result of the procedure depended on adapting the measurement, humidity and temperature to the raw materials in question, but it gave the opportunity to produce a heating product that was easy to pellet and had good storage properties.

Claims (6)

1. Procedure for the production of a heating product where particles of sewage sludge and particles of peat are pressed together to form agglomerates, in the form of granules, pellets or briquettes, characterized in that a) sewage sludge is dried to a dry matter content of 60 to 90 percent by weight and ground, b) that a long-fibre peat mass is dried to a dry matter content of 60-90 percent by weight, preferably 85 - 88 percent by weight and ground in a grinder (16) to a particle size of the range 0.2 to 10 mm, c) that a particle mixture is made in a mixing drum (24) with from 20 - 60 weight percent peat and 40 - 80 weight percent sewer lamp particles, and d) that the particle mixture is extruded to compress the particles. 2. Method in accordance with patent claim 1, characterized in that 30% by weight of peat and. 70 percent by weight sewage sludge. 3. Method in accordance with patent claim 1, characterized in that up to 10% by weight of the peat mass is replaced with other fibrous organic mass. 4. Method in accordance with one of patent claims 1 and 2, characterized in that the mixture of peat and sludge particles is dried, preferably together, before the pellet pressing. 5. Method in accordance with patent claim 3, characterized in that the dried mixture is pressed by hammering prior to pelletisation. 6. Method in accordance with one of patent claims 1 to 4, characterized in that water vapor is added to the particle mixture at the start of the pelletizing step, in order to regulate humidity and temperature.