GB1603605A - Garri preparation - Google Patents

Description

(54) GARRI PREPARATION (71) We, EAST CENTRAL STATE PROJECTS DEVELOPMENT AGENCY, a Body Corporate established under an Edict of East Central State of Nigeria, of 3 Independence Layout, P.O. Box 609, Enugu, Nigeria, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to improvements in the heating of the "garri frying" machines described and claimed in our British Patent Number 1 468 955 to which the reader is hereby directed to refer.

Heat plays a vital role in the conversion of cassava pulp to garri. If the heat is not sufficient, the cassava pulp will dry into a powder-like substance whose texture and taste are quite unacceptable. If the heat is too much, instant charring will result. Application of the correct temperature throughout the "garri frying" process produces garri, which is gelatinized cassava grains of the correct shape, size and flavour.

Traditionally the red glow from firewood fire is used to heat small bowls. If the pulp is too wet, the heating is gradual to effect some initial drying. At the correct condition of dryness, about 50% water content, the heating is increased to effect gelatinization and granulation and is then gradually reduced to effect some further dehydration.

The garri finishes with a moisture content of about seven per cent.

Measurements taken show that during the actual gelatinization and granulation, the temperature should be between 180"C and 220"C. If the pulp is too wet, this temperature can cause the pulp to form undesirable large lumps and also instant charring will occur. Various grades of garri actually result from various temperatures applied during gelatinization. A small quantity of palm oil may also be applied to aid granulation. It has also been found that the rate of heat transfer required during gelatinization can be obtained by radiation from a hot flame on to a metal trough holding the cassava pulp. This radiation is not affected by the black soot coating on the trough which is unavoidable when using a flame for heating.

In accordance with the invention of our above-mentioned British Patent 1 468 955, a machine for use in the conversion of cassava pulp into garri comprises an elongate trough in which the conversion is to be effected, a rotatable shaft mounted substantially on the axis of a curved portion of the elongate trough, and a plurality of blades carried around the circumference and along substantially the whole length of the rotatable shaft, with at least those blades located towards an inlet portion of the trough being formed with holes, and at least those blades located towards an outlet portion of the trough being L-shaped, when viewed in sections taken transversely to the longitudinal axis of said trough, and thereby including flanges, whereby, in use, the plurality of blades encourage, by stirring, a gradual movement along the curved portion of the trough of its contents away from said inlet portion, where a predominance of cassava pulp flows through the holes in the blades, and towards said outlet portion, where a predominance of garri is carried around the rotating shaft by the flanges on the blades.

When the above-defined "garri frying" machine was first built the problem of heating it centred around obtaining a suitable flame which should persist throughout the length of the trough and be concentrated at the side of the trough containing the cassava pulp. It was also necessary to be able to control the flame intensity and to have at least two zones, the gelatinization zone and the drying zone; the gelatinization zone having a trough temperature of 1800C to 220"C and the drying zone having a trough temperature of 100"C to 1500C.

Experiments with firewood, coal and butane gas failed to achieve the high standards which we had set ourselves.

According to the present invention, however, the above-defined "garri frying" machine further comprises a producer gas generator arranged to supply producer gas to at least two firing nozzles located at different positions along the length of, below and adjacent to the undersurface of the elongate trough, whereby in use respective flames resulting from burning producer gas emerging from said firing nozzles are employed to heat said adjacent undersurface of the elongate trough and thereby allow conversion of cassava pulp into garri.

Preferably, air vents are provided in a support for the elongate trough for controlling the length and/or the intensity of each flame; those air vents closest to the firing nozzles being relatively large and being primarily for controlling flame length, with the remainder of the air vents being relatively small and being primarily for controlling flame intensity.

There may be only two of the firing nozzles, one of which is located at the inlet end of the elongate trough, with the other being located mid-way along the length of the elongate trough. The firing nozzles may then be associated with respective chambers which both lie to one side, as viewed in transverse cross-section, of the elongate trough.

It is advantageous if the producer gas generator includes a reactor chamber to which coal can be fed automatically by gravity from a coal hopper to maintain a predetermined level therein, a water jacket located around an upper part of the reactor chamber for producing steam which can be directed towards a grate at the bottom of the reactor chamber, and a blower operable to direct air towards the grate so that, in use, the air, steam and hot coal react to form producer gas which is supplied to the firing nozzles. It is then particularly advantageous if that part of the reactor chamber above the coal level is connected via a tar condenser to a receiving vessel from which producer gas is distributed in use to each of the firing nozzles.

It should be appreciated that a machine according to the present invention may be used in association with another machine of similar construction which shares the output of the producer gas generator.

A machine according to the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure I is a vertical section through a producer gas generator; Figure 2 is a vertical section through a tar condenser; Figure 3 is a front elevation of a gas receiver; Figure 4 is an end view of the gas receiver shown in Figure 3; Figure 5 is a horizontal section through a firing chamber; and Figure 6 is a vertical section on the line A-A shown in Figure 5.

The gas generator of Figure 1 consists of a vertical cylindrical reactor chamber 14 made of mild steel. It is provided with ceramic insulation 7 and a water jacket 5 which is at the upper end of the chamber 14.

A cast iron grate 8 is positioned at the bottom of the chamber 14 and upon this grate rest pieces of bituminous coal up to a height of 4 feet. The coal is in lumps of approximately 1 inch although a mixture of powdered coal and various lump sizes up to 2 inches works very well.

A coal hopper 3 is positioned above the reactor chamber to which it is rigidly connected by a tubular piece 15 of about 1 foot diameter. This tubular piece 15 projects about 9 inches into the reactor chamber 14.

Coal feeds by gravity from the hopper 3, through the tubular piece 15 into the reactor chamber, in such a way that the level of coal above the grate in the reactor chamber is kept constant at an average of 4 feet. At the beginning of every shift 400 kilogram of coal, enough to last for one shift of 8 hours, is introduced into the hopper 3 which is then closed by a cover 1. A gasket 2 prevents gas leakage. During the shift the coal feeds automatically into the reactor chamber, and at the end of the shift, the cover 1 must be opened so that more coal can be fed into the hopper via a screw or elevator bucket (not shown).

The tubular piece 15 also serves to maintain an empty space free of coal at the top part of the reactor chamber. Two 4 inch pipes 16 lead out of this space and are connected together to another 4 inch pipe which leads the producer gas to a tar remover.

Below the grate 8 is an ash holder 10 also fabricated from mild steel. A blower (not shown) delivers air at the correct pressure and rate through a 1 inch pipe 9 which enters the ash holder tangentially. The tangential flow of air helps to precipitate the ash falling from the grate on to the bottom wall of the ash holder which slopes downwardly.

To start the plant, man-hole 13 is opened and red hot coal introduced on to the grate.

Then coal is dropped via the empty hopper 3 into the reactor chamber until subsequently both the chamber 14 and hopper 3 are filled up. This takes only a few minutes. The hopper 3 is closed. The man-hole 13 is then closed with a cover, which is also provided with a heat resistant gasket, and the blower is started.

At the end of the shift, the blower is turned off and the red hot coal maintains itself in the reactor chamber, ready for starting the following morning. So once lit, provided the producer is used daily or at intervals not exceeding 48 hours, the process can be started by merely turning on the blower.

For a reactor chamber of 1 yard diameter, the insulation helps to maintain the high temperatures required at the bottom part of the chamber. The water jacket 5, at the top part of the chamber, contains water whose level is indicated by level gauge 4. When the reactor is working, the water boils and produces steam which flows through a 2 pipe 6 into the ash chamber where it sprays onto the hot grate. The quantity of steam produced depends on the level of water in the chamber, and this is held just high enough to give the correct ratio of steam-air mixture for generating producer gas, which is a well known chemical reaction. This level of water is manually controlled by an operator who operates a stop cock 20 in a " pipe 19 which leads into the water jacket from a water mains. This arrangement has proved most satisfactory in cottage industries. Nevertheless, a simple automatic water level holder could be introduced.

During one shift, the ash that drops through the grate collects in the ash chamber 10 and at the end of the shift, this ash is released via a cover 12 into ash tray 17. The man-hole 13 is then opened and any more ash near the grate is further released by poking with a long thin rod.

After starting, the reactor takes about 20 minutes to heat up and attain the correct temperature and reaction equilibrium in which air, steam and hot coal react to form carbon monoxide, hydrogen, and unwanted compounds like carbon dioxide, nitrogen, tar and other impurities.

The hot gases flow from the reactor through the pipes 16, which converge before reaching the condenser or tar remover shown in Figure 2. This is a jacketed heat exchanger in which the hot gases enter tangentially, then flow downwards through a number of 1-inch vertical pipes 22, finally rising through a central 4-inch pipe 23. Cold water enters the jacket through pipe 25 and leaves through pipe 26.

The tar and other condensate collect at the bottom of the chamber from where they are continuously removed by a hydraulic trap formed by two concentric pipes 28 and 29. The condensate collects in 29 and overflows through pipe 30 into a waste container (not shown). Stop cock 27 is left continuously open. The head of liquid in the pipe 29 is 15 inches, which is slightly higher than the static pressure developed by the blower that supplies air to the gas producer.

Initially the pipe 29 is filled with water. The condensate that collects at the bottom of the heat exchanger is forced into the pipe 29 by the pressure in the chamber, and being lighter than water, it rises to the top and overflows.

The cold water pipe 25 comes from the mains. The flow of water is regulated by a stop cock. The hot water leaving at 26 goes either to waste or is utilised in washing cassava or containers.

The stop cock 27 can be closed to detach and clean the hydraulic trap during operation.

The gases leaving the tar condenser flow along the pipe 23 and continue along a horizontal pipe 37, shown in Figure 3, to a flaring point where excess gas is burnt off.

When starting up the gas producer, the initial gases released are not suitable for use as fuel, and these are burnt off at the flaring point by the use of a small open coal fire immediately beneath the pipe outlet (not shown) located beyond stop valve 38. If this was not burnt off, the area would be polluted with thick obnoxious fumes. After the gas producer has attained the correct temperature, the gases can be directed via pipe 31 into the gas receiver of Figures 3 and 4, shown supported on a stand 39.

The gases enter tangentially through the pipe 31 and leave tangentially through a number of 12" pipes 32. Each of the pipes 32 leads to a firing point. The tangential flow of gases causes a better heat exchange between the gases and the wall of the gas receiver.

Any tar or liquid still contained is deposited by centrifugal action on the wall of the receiver and flow down pipe 33 to another hydraulic trap 35 with overflow. Cover 36 can be removed to clean out the receiver.

The tangential flow also minimises loss of head. The capacity of the gas producer is preferably designed to support two "garri frying" machines. Where only one machine is in use, the excess gas must be continuously run off through the pipe 37 and flared. It has been found that if the normal rate of gas flow should be reduced by half, the gas producer would not give good quality fuel.

From the receiver, the producer gas now flows to the "garri frying" machines. One machine, shown in Figures 5 and 6, requires two burners. The machine consists of an elongate U-shaped trough 50 with flanges 53 that rest on brick side walls 48. Inside the trough there is a longitudinal shaft with blade assembly 52. This machine has been amply described in our above-mentioned British Patent No. 1 468 955. The blades agitate and propel the cassava pulp from the inlet end of the trough to the outlet end. In Figure 6, it can be seen that pulp 62, owing to the action of the blades, collects largely at the bottom left half of the U-trough, which is where the heat is concentrated by the following arrangement.

Beneath the trough 50, which is about 15 feet long, is a long firing chamber formed by the brick side walls 48, ends walls 58 and 59, the trough body and a brick floor. This firing chamber is further divided into two by a longitudinal steel plate 46 which is welded on to the bottom of the trough and projects into the brick floor. This plate is cut away at two points 49 and 49A for the gases to be able to flow therethrough. A narrow brick wall 57 divides one of the longitudinal chambers into two equal chambers 54 and 55.

Two of the pipes 32 lead the gases from the receiver to respective firing nozzles 44 and 45. The first nozzle 44 is about one inch diameter and stops at an opening 40 which is provided in the end wall 58. The flow of gas through the nozzle can be controlled manually by simple stop-cocks 42.

The gas flows out of 44 at some speed and sweeps across the chamber 54. It also picks up some air through the wall opening 40.

The air picked up can be regulated by partially closing the opening 40 with bricks.

This partial closing of opening 40 ensures that the air mixes with the gas gradually, thus yielding a long flame that persists throughout the length of the chamber-54.

Additional air holes 41. provided in the wall 48 along the length of the chamber, can be used to improve slightly the length of the flame but primarily to control flame intensity and thus ensure complete combustion and absence of smoke. If the port 40 is made larger, the flame will be shorter. If the port 40 is almost completely closed, the flame will move farther inside the chamber 54 such that combustion will actually commence about 2 feet from the opening 40. In this case more of the, air holes 41 must be opened and these air holes 41 are controlled by shaped bricks which are used to close or open them. This latter arrangement is used when the pulp is wet, so that some initial drying occurs at the trough end. Again the flame obtained is long and the low calorific value of producer gas makes the flame temperature just ideal for this application.

After combustion in the chamber 54, the gases pass through the port 49 into the chamber 56 and flow out through exit 47 into a chimney.

The chamber 55 is fired by the second nozzle 45. The pipe bringing the gas enters the chamber 54 through a bent tube 43 and just projects into the chamber 55 through a small hole in the brick wall 57. The nozzle 45 is 3/4 inch diameter and the gases flowing out of it collect the necessary air through an opening 40A in the brick wall 48. Much the same thing happens during combustion except that a smaller flame is obtained. The trough above this flame is actually the drying chamber for drying the garri which is largely formed above chamber 54.

The gases in 55 flow through the opening 49A into 56 and out to the chimney. The cassava pulp enters the trough just above the nozzle 44. The pulp is agitated and moved along the trough, first over 54 where gelatinization and granulation largely occur, then over 55 for drying. The pulp collects mainly on the bottom half of the trough above the chambers 54 and 55 and therefore receives direct heat radiated on to the trough there. By the time the gases enter 56, the flame has ceased and the gases impart heat to the trough mainly by conduction.

There is little pulp at this side of the trough above 56. There is a sort of heat balance which prevents the mild steel trough from warping or buckling.

The only moving part of the whole firing system is the blower that supplies air to the gas producer. Control is manual. The gas flow rate and the burner nozzles are exactly determined to give the required heat at the desired rate of garri production so that very little manipulation of the control stop-cocks 42 is required. When the cocks are fully open, the correct temperatures are quickly attained and kept constant by feeding cassava pulp at a constant rate into one end of the trough. The operator peeps occasionally into the trough to ensure that the thickness of the pulp bed is as desired. If not he must quickly add more pulp or reduce the feed rate of the pulp until the correct pulp bed thickness is attained.

A few small pieces of brick 60 are positioned on the floor of the firing chamber just in front of the nozzles to serve as flame holders. Fire is applied manually by a torch or burning rag to light the gas which thereafter continues to burn on its own.

The openings 40 and 40A, with the additional air holes 41, together constitute air vents for controlling the length and/or the intensity of each flame; those air vents closest to the firing nozzles (openings 40 are 40A) being relatively large and being primarily for controlling flame length; with the remainder of the air vents (air holes 41) being relatively small and being primarily for controlling flame intensity.

It will be appreciated that, although the above-described arrangement is that which is currently preferred, various modifications could be readily made if desired in particular applications. For example, there may be more than two of the firing nozzles located at different positions along the length of, below and adjacent to the undersurface of the elongate trough. Moreover, there are preferably two of the "garri frying" machines, of similar construction, which share the output of a single producer gas generator.

WHAT WE ClAIM IS: 1. A machine according to claim 1 of British Patent No. I 4(8 (J55, and further comprising a producer gas generator arranged to supply producer gas to at least two firing nozzles located at different positions along the length of, below and adjacent to the undersurface of the elongate trough, whereby in use respective flames resulting from burning producer gas emerging from said firing nozzles are employed to heat said adjacent undersurface of the elongate trough and thereby allow conversion of cassava pulp into garri.

2. A machine according to claim 1, in which air vents are provided in a support for the elongate trough for controlling the length and/or the intensity of each flame.

3. A machine according to claim 2, in which those air vents closest to the firing nozzles are relatively large and are primarily for controlling flame length, with the remainder of the air vents being relatively small and being primarily for controlling flame intensity.

4. A machine according to any preceding claim, in which there are only two of the firing nozzles, one of which is located at the inlet end of the elongate trough, with the other being located mid-way along the length of the elongate trough.

5. A machine according to claim 4, in which the firing nozzles are associated with respective chambers which both lie to one side, as viewed in transverse cross-section, of the elongate trough.

6. A machine according to any preceding claim, in which the producer gas generator includes a reactor chamber to which coal can be fed automatically by gravity from a coal hopper to maintain a predetermined level therein, a water jacket located around an upper part of the reactor chamber for producing steam which can be directed towards a grate at the bottom of the reactor chamber, and a blower operable to direct air towards the grate so that, in use, the air, steam and hot coal react to form producer gas which is supplied to the firing nozzles.

7. A machine according to claim 6, in which that part of the reactor chamber above the coal level is connected via a tar condenser to a receiving vessel from which producer gas is distributed in use to each of the firing nozzles.

8. A machine according to any preceding claim in association with another machine of similar construction which shares the output of the producer gas generator.

9. A machine according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. preferably two of the "garri frying" machines, of similar construction, which share the output of a single producer gas generator. WHAT WE ClAIM IS:

1. A machine according to claim 1 of British Patent No. I 4(8 (J55, and further comprising a producer gas generator arranged to supply producer gas to at least two firing nozzles located at different positions along the length of, below and adjacent to the undersurface of the elongate trough, whereby in use respective flames resulting from burning producer gas emerging from said firing nozzles are employed to heat said adjacent undersurface of the elongate trough and thereby allow conversion of cassava pulp into garri.

2. A machine according to claim 1, in which air vents are provided in a support for the elongate trough for controlling the length and/or the intensity of each flame.

3. A machine according to claim 2, in which those air vents closest to the firing nozzles are relatively large and are primarily for controlling flame length, with the remainder of the air vents being relatively small and being primarily for controlling flame intensity.

4. A machine according to any preceding claim, in which there are only two of the firing nozzles, one of which is located at the inlet end of the elongate trough, with the other being located mid-way along the length of the elongate trough.

5. A machine according to claim 4, in which the firing nozzles are associated with respective chambers which both lie to one side, as viewed in transverse cross-section, of the elongate trough.

6. A machine according to any preceding claim, in which the producer gas generator includes a reactor chamber to which coal can be fed automatically by gravity from a coal hopper to maintain a predetermined level therein, a water jacket located around an upper part of the reactor chamber for producing steam which can be directed towards a grate at the bottom of the reactor chamber, and a blower operable to direct air towards the grate so that, in use, the air, steam and hot coal react to form producer gas which is supplied to the firing nozzles.

7. A machine according to claim 6, in which that part of the reactor chamber above the coal level is connected via a tar condenser to a receiving vessel from which producer gas is distributed in use to each of the firing nozzles.

8. A machine according to any preceding claim in association with another machine of similar construction which shares the output of the producer gas generator.

9. A machine according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.