GB2405132A - I/C engine driven extruder heated by exhaust gas - Google Patents

Abstract

A single or multi-screw extruder is driven by an internal combustion engine 31 via a mechanical or hydraulic linkage 32, wherein thermal energy from the engine is transferred to a heating system of the extruder by supplying at least a portion of the engine exhaust gases via insulated ducting to heat exchangers mounted on or in a barrel of the extruder. The engine and extruder may be mounted on a wheeled vehicle which may also be powered by the engine. The vehicle may be a tractor 30, and the extruder may be powered by the tractor engine through its power take-off system. Burners supplied with flammable organic substances may be used to raise the temperature of the exhaust gas. The exhaust gas may be pressurised by fans 4 between the engine and the heat exchangers.

Description

1 2405 132

Title of the Invention

Internal Combustion Engine Driven Extruder with Exhaust Gas Barrel Heating

Field of the Invention

The invention relates to improvements in the energy efficiency of extrusion equipment which also enables its use in locations without access to high capacity electricity supplies.

Background of the Invention

Modern extrusion equipment almost invariably now uses electric motors and heating systems and although developments in power electronics have enabled these to make ever more efficient use of the electricity supplied to them the efficiency of the complete system including the electricity generating station as well as the transmission grid is typically less than 30%.

Furthermore a very high capacity supply is required, which can be prohibitively expensive in rural locations and developing countries or where use of the extrusion equipment is required only for a relatively short period of time.

A common solution here is to make use of an internal combustion engine driven electrical generator which does illustrate the lamentable inefficiency of converting energy from chemical to thermal then to mechanical into electrical in order to finally produce heat and mechanical power.

On the other hand large scale combined heat and power stations which supply both electricity and district space heating are well known and can have efficiencies approaching 80%.

Smaller combined heat and power stations using internal combustion engines can achieve similar efficiencies by using both the high temperature exhaust gases and lower temperature cooling water to provide space heating.

However the exhaust gases which are typically in the region of 650 C to 700 C as they leave the cylinder could be used directly to maintain much higher temperatures if transported via an insulated manifold.

Particularly in the rural environment there are many operations which can only be economically performed in the farm fields themselves.

Modern tractors however, whilst not equipped with large electrical generators, do have the ability to supply high torque variable speed rotational drive via their power take off systems from their powerful diesel engines.

One of the major applications anticipated for the invention is the recovery of grain straw through its processing in field to pellets, which has the potential to provide millions of tonnes of biomass fuel in the UK alone.

The conventional approach to this problem involves partial compaction of the straw to bales, its transport to a staging area followed by high intensity compaction to briquettes or pellets using stationary ram or screw extruders.

This is very costly in comparison to collecting and processing the straw in a single operation out in the held where the crop has been grown.

Recent work on the use of extrusion technology in biomass production as documented for instance in Field Document No. 46 "Biomass Briquetting Technology and Practice" (1996) from the Regional Wood Energy Development Programme in Asia of the Food and Agriculture Organization of the United Nations has emphasized the advantages of strongly heating the biomass to improve both its extrusion and combustion properties. However they describe permanently installed systems particularly ones using furnaces to heat oil as a transfer medium.

Whilst there are some tractor mounted extruders these are unheated with limited warming of the biomass resulting from frictional effects and whilst DE4214111 does describe a pelletising system integrated into a combine harvester using relatively low grade heat recovered from the engine via water or oil it has only a simple unheated auger feed mechanism rather than a compacting extruder.

Thus the invention enables the enhanced processing resulting from significant heating whilst improving the overall efficiency of the process by utilising thermal energy that would otherwise be wasted.

Object of the Invention The basic object of the invention is to provide an extruder with improved energy efficiency that is capable of being operated without access to high capacity electrical supplies suitable for, but not limited to, the compaction of biomass to pellets or briquettes.

Summary of the Invention

An extruder is provided comprising: i) A hollow barrel containing one or more extruder screws.

ii) An internal combustion engine.

iii) A suitable drive train allowing the extruder screw/screws to be rotated by the internal combustion engine.

iv) An insulated exhaust manifold and transfer ducting system providing a continuous flow gap from the cylinder exhaust ports to one or more heat exchange surrounding and in thermal contact with the extruder barrel.

v) A means of regulating the volume of exhaust gases flowing into and through each heat exchangers independently of each other.

vi) A means of safely discharging any exhaust gases not required by the heat exchangers to the atmosphere.

vii) A means of supplying and regulating the volume of cooling air flowing into and through each heat exchangers independently of each other.

viii) A means of sensing the barrel temperature beneath each heat exchanger and using this information to regulate the flow of exhaust gas and cooling air through each such heat exchanger so as to maintain the set temperature provided to the control system by the extruder operator.

Advantages of the Invention The principle advantages of the invention are that by using both the mechanical and thermal energy extracted from the fuel used a much higher overall energy efficiency can be achieved and the unit can operate independently of a high capacity electrical supply system and is thus suitable for operation in farm fields where biomass is grown.

Preferred or Optional Features of the Invention In its preferred form the extruder is mounted on a trailer towed by a internal combustion engine powered tractor, however it would equally be possible to use a separate engine or integrated into a purpose built vehicle. Likewise the invention could be statically mounted where the main reason for using the invention is to overcome a lack of electrical grid capacity rather than the need to make the extruder mobile.

Looking then at the preferred form the existing exhaust system is modified by fitting an insulated manifold and transfer ducting to take the exhaust gases to the rear of the machine where it is connected to the exhaust gas ducting on the trailer by a gas tight section that is either flexible or telescopic to such an extent that the relative motion between tractor and trailer can be accommodated.

Exhaust gases then flow past the inlet to a pressuring fan which runs continuously and draws in that portion of the exhaust gas stream that is required for the heating system at any particular moment. Any exhaust gases not required then flow up a discharge pipe and are vented to atmosphere. In this way the back pressure on the diesel engine is not subjected to large pressure variations as the proportion of exhaust gases being used in the heating system changes providing that the back pressure on the discharge pipe is not large in comparison to the back pressure in the transfer ducting since the pressure at the pressuring inlet fan will be held effectively at atmospheric pressure.

Stabilisation of the exhaust pressure at the engine exhaust manifold is important for the efficient operation of the motor. Control of this pressure could also be achieved by the use of a set of valves and pressure measurement devices linked to an electronic controller although this would be inherently more complex and costly.

To provide heating for the extruder exhaust gases pass from the pressurising fan to a distribution duct which runs the length of the extruder barrel and has openings in it that allow the gas to flow to individual heat exchange assemblies, which are provided spaced apart along and in good thermal contact with said barrel.

A motorised valve is required to regulate the flow of exhaust gas from the distribution manifold to the heat exchanger assembly and in the preferred form this is a three position unit enabling it to additionally allow cooling air to flow into the heat exchanger and block the flow of both as required.

In this way only a single inlet and outlet manifold is required on the heat exchanger assembly to maintain symmetric gas flow in both directions about the barrel which in the preferred form has a circular cross-section, although they can have any desired shape should this be necessary for the operation of the extruder itself.

Thus in the preferred form the heat exchangers themselves can be manufactured from plain tubular aluminium castings suitably turned to provide a close fitting interior surface for the barrel wall and equipped with a series of spaced apart fins by cutting deep grooves into the exterior surface. Parting the tube down one or both sides then allows sufficient movement of the interior surface to allow it to be clamped onto the barrel using bolts or other means to close the gap or gaps so provided.

Cooling air is also provided via a pressuring fan and distribution manifold and in the preferred form the pressure in the cooling distribution manifold is held at a similar level to that in the exhaust distribution manifold to prevent back flows where cooling and exhaust air are discharged into a common manifold.

The pressuring fans themselves can either be driven mechanically from the extruder drive train or electrically providing the tractor has sufficient generating capacity.

The outlet manifolds from the heat exchanger assemblies discharge into a collection manifold with a discharge pipe to atmosphere. Depending on the process conditions required this may receive exhaust gas and/or cooling air from heat exchanger assemblies.

Looking at the effective heating power of the exhaust gases it is clear that the energy Imparted to the extruder by any given amount of exhaust gas is dependent on the fall in temperature from inlet to outlet. Thus as the extruder warms, the heating power of each heat exchanger assembly falls resulting in a maximum equilibrium temperature where the heat losses to the material being processed and to the environment equal those extracted from the exhaust gases.

In oil heated extrusion systems a similar upper limit exists although this is defined by the temperature stability of the oil used.

Whilst the upper temperature of the exhaust gases leaving the engine block is limited by the materials used in its construction it can be further heated before entering the heat exchanger assemblies by use of an auxiliary burner or set burners.

Although not as efficient as using the waste heat in the exhaust stream it is nevertheless thermodynamically very efficient in comparison to using a burner to provide the entire thermal energy since the energy contained in the gases discharged to atmosphere would still come predominantly from the combustion needed to drive the motor.

The most flexible and efficient system would be to provide individual burners for each of the heat exchanger assemblies or just those where particularly high temperatures may be required, however if only limited use of such heating is to be made it may be more cost effective to use a single burner venting into the exhaust gas distribution manifold.

Since the invention relates to the means of driving and heating the extruder it is suitable for use on any type of machine, be it single, coor counter rotating twin or multiple screw, however in the preferred form it is used in combination with single or counter rotating twin screw, which have excellent compaction capacity in relation to biomass.

Once compacted within the extruder the biomass is discharged through a die which determines the profile of the material before it is cooled and cut to the desired length by suitable means. In the preferred form the final form of the biomass is pellets of a size that allows them to be conveyed, transported and stored using standard agricultural grain handling equipment.

Brief Description of the Drawings

Figure 1 is a side view of the preferred form of the invention.

Figure 2 is a perspective view of the extruder with the external insulation removed.

Figure 3 is a perspective view of the extruder with the cooling and exhaust gas inlet manifolds removed to give an unhindered view of the heat exchanger assemblies.

Figure 4 is an exploded perspective view of heat exchanger assembly 9.

Figure 5 is an end view of the extruder.

Figure 6 is a perspective sectional view of the inlet selector valve and shroud.

Figure 7 is a side sectional view showing the various positions of the inlet selector valve.

Figure 8 is a perspective sectional view of the extruder showing the disposition of the barrel ports and extruder screw.

Detailed Description of the Drawings

Referring to figure 1 the extruder is mounted on a trailer 36 and drawn by a tractor 30. The exhaust gas transfer manifold runs from the engine 31 to the trailer where it is attached to the distribution system and the drive shaft 32 likewise runs from the gear box 37 through to the extruder on the trailer where it provides rotational drive to the screw via the drive couple feature 1 8a.

The material to be extruded is fed into the extruder via the feed hopper 24 and discharges via the die 35 to the pelletiser and cooler 33 which in its turn discharges the finished product into the storage bin 34.

Referring to figure 2 exhaust gases from the internal combustion engine pass along the transfer manifold 1 to the exhaust gas pressurising fan inlet manifold 3.

Depending on the volume of exhaust gas flowing through the exhaust gas pressuring fan 4 and along the exhaust gas distribution manifold 5 some or all of the exhaust gas vents to atmosphere via the exhaust gas bypass vent pipe 2.

Cooling air is likewise drawn into the cooling air pressuring fan 7 via the cooling air inlet manifold 6 supplied to the cooling air distribution manifold 8.

Referring to figure 3 the barrel is equipped with a series of spaced apart heat exchanger assemblies 9, 10, 11, 12, 13, 14 & 15 through which either exhaust gas or cooling air from the respective distribution manifold is allowed to flow, depending on whether the barrel temperature under a given heat exchanger assembly is too low or high, before being discharged to atmosphere via the outlet collection manifold 16.

Referring to figure 4 the component parts of heat exchanger assembly 9 are shown as an example. This comprises an inlet selector valve sub- assembly with cooling air inlet 9a, exhaust gas inlet 9b, selector rotor 9c and outlet port 9d discharging into the shroud inlet manifold Be on the bottom shroud half Of which covers the bottom finned heat exchanger element 99 and is held in place around the barrel so as to join to the bottom finned heat exchanger element 9h and its shroud 9i with outlet manifold 9j.

The connection of the valve assembly to the other components is shown in detail in figure 5. Here the pressurised exhaust gas 5 and cooling air 8 distribution manifolds can be seen located to either side of the inlet selector valves. In the end view shown only valve 9 is visible with the cooling air inlet 9a and exhaust gas inlet 9b connecting to the respective distribution manifolds. With the selector rotor in the shut position no gas flows through the outlet port otherwise depending on the position of the selector rotor 9c either exhaust gas or cooling air will flow into the shroud inlet manifold 9.

The exhaust gas or air flow splits into streams contained by the fins on the heat exchanger elements Of and 99 and the shrouds 9h and 9i emerging into the outlet manifold 9j to discharge into the outlet collection manifold 16 which vents to atmosphere via the outlet pipe 17.

Figure 6 shows a cutaway of a selector valve and in particular the flow gap formed by the intersection of two holes set at 90 to each other about the circumference bored towards the centre of the rotor. The rotor is turned by the actuator motor Ok to change the connection between the distribution manifold 5 and 8 and the outlet port 9d.

Looking at figure 7 the three functional positions of the selector valve are shown.

Figure 7a shows the rotor 9c providing a flow gap from the exhaust inlet 9d to the heat exchanger allowing said gases to pass through the assembly heating the barrel section beneath it.

Figure 7b shows the rotor 9c rotated through 90 providing a flow gap from the cooling inlet 9a to the heat exchanger allowing said gases to pass through the assembly cooling the barrel section beneath it.

Figure 7c shows the rotor 9c rotated through a further 90 interrupting the flow gaps from both the exhaust and cooling air inlets which means the barrel receives neither exhaust gases nor cooling air. À 13

As previously mentioned in the preferred form the pressure in the exhaust gas distribution manifold 5 and cooling air manifold 8 is held approximately equal, which limits leakage between the two via the valve.

In the drawings a single screw extruder is shown although this could equally be any multiple screw machine since the invention relates to the method of heating and driving the extruder rather than the particular functionality of the extruder itself.

Figure 8 shows the extruder screw 18 with drive coupling feature 18a, to which the drive train from the internal combustion engine is attached, and barrel 19 with process material entering the extruder via feed port 20 from where the rotary motion of the screw relative to the barrel causes it to be conveyed in the direction of the discharge end of the extruder. As it does so it is heated to a suitable temperature by both the heat provided by the heat exchanger assemblies and also by the effects of mechanical energy resulting in frictional and Reformational processes.

In doing so volatile materials can be released from the process materials and these are vented via the vent ports 21 and 22.

The suitably conditioned material emerging from the discharge opening 23 can then be formed by a die to the required shape and suitably cooled and cut by standard means not shown here.

Claims (12)

1. Claims 1. An single or multi-screw extruder equipped with an internal

   combustion engine which provides rotational drive for the screw(s) via a mechanical or hydraulic drive train and thermal energy to the heating system by supplying a portion or all of the engine exhaust gases via suitable insulated ducting to heat exchangers mounted on and in thermal contact with the extruder barrel at such times as thermal energy Is required to raise or maintain the barrel or process material temperature.
2. 2. An extruder as described in claim 1 where the internal combustion engine and extruder are mounted on a wheeled vehicle which may also be provided with motive power by said engine or an entirely separate one.
3. 3. An extruder as described in claim 1 where the internal combustion engine forms part of an agricultural tractor and drives the extruder via a detachable or permanent coupling to its power take-off system.
4. 4. An extruder as described in claim 3 where the extruder is detachably or permanently mounted on the tractor's three point linkage or towed on a trailer.
5. 5. An extruder as described in any of the previous claims where the exhaust gas is pressurised by one or more fans or similar rotating aerodynamic features located in the flow gap between the engine and the heat exchangers.
6. 6. An extruder as described in any of the previous claims where cooling of the extruder barrel is provided by passing atmospheric air through heat exchangers mounted on the extruder barrel.
7. 7. An extruder as described in claim 6 where the cooling air is pressurised by one or more fans or similar rotating aerodynamic features.
8. 8. An extruder as described in any of the previous claims where one or more of the heat exchangers is equipped with a system of valves that enables the extruder control system to allow either exhaust gases or cooling air to flow through said heat exchangers or to isolate said heat exchangers from both so as to maintain the temperature of the barrel or process material below said heat exchangers as measured by suitable means at a level specified by the extruder operator.
9. 9. An extruder as described in claim 8 where a single rotary position valve on each heat exchanger is used to control the flow of gases in said heat exchanger.
10. 10.An extruder as described in any of the previous claims where one or more burners supplied with oil, diesel, kerosene, liquid petroleum or other such flammable organic substance gas are used to raised the temperature of the exhaust gases coming from the internal combustion engine.
11. 11.An extruder as described in claim 10 where the burners are provided such that they can raise the temperature of the exhaust gases being supplied to individual heat exchangers independently of each other.
12. 12. The use of an extruder as described in any of the previous claims to manufacture briquettes or pellets from biomass where said manufacture takes place at the location where the biomass is grown.