GB2122864A - Improvements in straw treatment - Google Patents

Abstract

Straw/fodder conversion apparatus comprises a sealable chamber for receiving straw to be treated in a heated ammonia laden atmosphere. Ammonia gas is fed to the chamber via an external expansion tank which receives liquid ammonia under pressure from a liquefied source. The liquid ammonia expands and boils in the tank, and a series of baffles are provided in the tank to increase the surface area in the tank exposed to liquefied ammonia and so promote boiling.

Description

SPECIFICATION Improvements in straw treatment Field of Invention This invention relates to straw treatment and concerns apparatus for treating fibrous materials such as straw to produce useful fodder for livestock.

Background to the Invention Research work published by the Biotecknisk Institute, Kolding, Denmark, shows that treatment of straw, i.e. the waste from cereal crops, and like fibrous materials (for convenience such materials are hereinafter generally referred to as 'straw') by exposure to a heated ammonia laden atmosphere results in conversion of the straw to useful fodder for livestock. The ammonia attacks the straw, breaking down the fibrous content (and so improving digestibility) and simultaneously substantially increasing the protein content, thus increasing its food value considerably.

As a direct result of this research work, conversion apparatus was developed which comprised a sealable bin having heating means and to which liquefied ammonia was directly supplied from a pressurised source. Such apparatus was marketed in Denmark in 1976.

With the known apparatus, because liquefied ammonia was introduced directly into the bin, temperatures within the bin dropped dramatically on expansion of the liquefied ammonia on introduction to the bin. Consequently, a considerable amount of energy, e.g. electricity, was needed to raise the temperature inside the bin to the required level.

This problem was partially overcome by a later design of converter as disclosed in GB 2094127.

This apparatus comprises an expansion tank external of the bin and to which ammonia under pressure from a liquefied source is fed. The ammonia cools on initial expansion into the tank and boils in the tank to produce an ammonia atmosphere which expands naturally through a supply duct communicating with the bin interior.

Provision of an external expansion tank means that ammonia is supplied to the bin at a higher temperature than would otherwise be the case. In this desiyn, however, heating of the bin is effected by means of a fan-assisted air circulatory system, which includes a warm air duct passing through the expansion tank to cause boiling of ammonia.

As a result, in use the circulating air in the duct is cooled by the expanding ammonia. This cooled air is then pumped back into the bin and the potential savings in energy are therefore not fully realised.

Summary of the Invention The present invention provides apparatus for treating straw comprising a sealable chamber for receiving straw to be treated, means for maintaining an ammonia laden atmosphere in the sealed chamber, and an expansion tank external at the chamber for receiving liquid ammonia under pressure and wherein ammonia expands and boils prior to passage to the chamber, the expansion tank being provided with a series of internal baffles.

By providing baffles in the expansion tank the surface area inside the tank exposed to liquefied ammonia is increased and as a result boiling of the ammonia is promoted. The baffles are designed to provide sufficient surface area within the tank so that in normal circumstances the liquid ammonia will expand and boil off without the need for supplementary heat.

The expansion tank is, however, nevertheless preferably supplied with heating means in the form of an electrical heating element for providing a low level of heat to assist in boiling of ammonia in cold conditions, say -1 50C or below.

Preferably heated air/ammonia mixture is circulated through the sealed chamber or bin by a high capacity fan which is connected to a heater box containing electric elements, and the temperature inside the bin is controlled by a thermostat adjustable to the size of the bin and the type of straw being processed.

Conveniently steel ribs are fitted to the floor of the bin, onto which the straw is laid. Air/ammonia mixture is thus able to circulate around and through the straw, and by employing a high volume of gas, so the use of complicated ducts is rendered unnecessary. This also means that the wall, which is preferably of double skin construction, needs only to 2" (50 mm) thick rather than the 3" (76 mm) or 4" (101 mm) thicknesses characteristic of previous designs, with no reduction in thermal efficiency.

The apparatus is used to treat straw with ammonia to produce animal fodder by circulating a heated mixture of air and ammonia through a volume of straw contained within the sealed treatment chamber for an initial treatment period, typically of the order of 1 6 hours, and then circulating fresh air through the treatment chamber for a final treatment period, typically about 4 hours According to a preferred feature of the invention the fresh air enters via a solenoid operated valve at the top and near the front of the chamber and stale air is exhausted through a similar valve, situated at the top of the chamber at the rear.

Conveniently the fan for circulating the air has an outlet which is situated at the rear of the chamber and the exhaust valve is conveniently located over the fan outlet.

One embodiment of apparatus embodying the invention will now be described, by way of example, with reference to the accompanying drawings.

In the Drawings Figures 1, 2, and 3 are orthogonal views of an expansion tank of apparatus embodying the invention; Figure 4 is a cross-section on line A-A of Figure 2 to an enlarged scale; Figures 5 to 7 are orthogonal views of a fan and heater unit of apparatus embodying the invention; Figure 8 is a top plan view of a hot air inlet to the treatment chamber of the apparatus; Figure 9 is a cross-section on line A-A of Figure 8; Figure 10 is a front view of part of Figure 9; Figures 11 (a) and 11 (b) shows details of solenoid vent valves of the treatment chamber, in closed and open modes respectively; and Figures 12(a) and 12(b) illustrate the flow of air and ammonia in the treatment chamber.

Detailed Description of the Drawings In outline, the illustrated apparatus comprises an expansion tank 10 (Figures 1 to 4) to which ammonia from a liquefied source is supplied. The resulting gaseous ammonia passes to a fan and heater unit 30 (Figures 5 to 7) to which air is also supplied from a straw treatment chamber 54 and the resulting heated ammonia/air mixture is then passed to the straw treatment chamber 54 (Figures 8 to 10). The mixture is circulated through the unit 30 and chamber 54 for an appropriate treatment time to cause conversion of straw to fodder, and the chamber is then cleared of ammonia by circulation of fresh air.

The expansion tank 10 shown in Figures 1 to 4 is of generally rectangular configuration, having appropriate length, width and height dimensions x, y and z. The tank includes an ammonia inlet 12 in one end wall through which liquefied ammonia is supplied from a pressurised source, e.g. a commercially available sealed cylinder, canister or other holder thereof. Valve means (not shown) is provided for regulating the supply of ammonia to the apparatus.

As shown in Figures 2 and 4, the inlet 12 communicates with an apertured spray bar 1 8 for distributing liquid ammonia in the tank. The tank also includes outlet pipes 14 in the upper wall and a drain plug 1 6 in the lower wall.

A series of inclined baffles 20 are provided in the interior of the tank, the baffles increasing the surface area inside the tank exposed to the liquefied ammonia and so enhancing boiling. The baffles 20 are conveniently formed by folding of the side wall of the tank, and are provided with fins 22, typically 3" (76 mm) in width, for improving heat transfer.

Gravity flow drip trays 24 are provided below the baffles 20 for directing any non-evaporated liquid ammonia to the next below inclined baffle 20.

Further fins 26 are provided at the bottom of the tank.

The baffles are designed to provide sufficient surface area within the tank, with good heat exchange between the interior and exterior of the tank, so that in normal circumstances in equable climates, such as in the UK, liquid ammonia will expand and boil off without the need for supplementary heat. It is found that total energy consumption is reduced by an average of 20% as compared with known apparatus. The expansion tank is, however, nevertheless preferably supplied with heating means in the form of an electrical heating element (not shown) for providing a low level of heat to assist in boiling of ammonia in cold conditions, say -1 50C or below.

In use, liquid ammonia under pressure is supplied to the tank via inlet 12 and spray bar 18, and expands and boils in the tank, with the ammonia gas leaving the tank via outlets 14.

Ammonia leaving the tank 10 enters a fan and heater unit 30 illustrated in Figures 5 to 7. Unit 30 comprises a housing 34 having a safety inspection hatch 36 at one end thereof. A series of electrical heating elements 32, typically six, are situated within the housing 34, the element being inclined towards the direction of gas flow, as shown, for safety.

Ammonia from tank 10 enters housing 34 via inlets 31. The housing 34 is also supplied with air which is circulated from the straw treatment chamber 54, the air entering the housing via an inlet (not shown) in plate 38, as represented by arrow X in Figure 6. A square section duct 42 (Figure 7) conveys the resulting air/ammonia mixture to heater elements 32.

After passing over the heater elements, the heated air/ammonia mixture enters a high capacity fan unit 44 driven by a motor 46, to be passed to straw treatment chamber 54, as indicated by arrow Y in Figure 6.

Referring now to Figures 8 to 10, the fan and heater unit 30 is bolted via mountings 49 onto a plate 48 forming part of the rear wall of a straw treatment chamber 54. Chamber 54 is of double skin construction, with approximately 2" (50 mm) between the skins. The chamber may be rectangular, cylindrical or any other convenient shape, and includes a door (not shown) which can be opened for insertion of straw to be treated and then sealed closed.

The chamber includes a series of steel ribs (not shown) on the floor and on which straw 56 (normally baled) can be laid so that gas is able to circulate around and below the straw.

Heated air/ammonia mixture is passed from the outlet of fan 44 via a flexible hose or angled duct or pipe (not shown) and enters chamber 54 via an inlet 64. The mixture then passes to a duct 50 (Figure 9) inside the chamber 54, which directs the incoming mixture towards a deflector 52 at the top of the chamber. After passing around and below the straw 56, the gaseous mixture passes as indicated by arrow 58 in Figure 9 to an outlet duct 60 to leave the chamber 54 via a square outlet 62 (Figure 10). Outlet 62 registers with the inlet in plate 38 (Figure 6) for recirculation of the mixture through unit 30.

In the illustrated embodiment the inlet 64 for introducing air/ammonia mixture to chamber 54 is located above the outlet 62. However, in some cases it is preferred to reverse the arrangement of flow. This can be achieved by changing electrical connections to the fan unit. Alternatively, the whole of the fan unit 30 mounting plate 48 can be mounted upside down to achieve the same effect.

The upper part of chamber 35 is provided with two similar solenoid operated valves 66, designated 66' and 66" in Figures 12(a) and (b).

The valves are used for circulating fresh air through the chamber, as will be described below.

The construction of each valve 66 is illustrated in Figures 11 (a) and (b) and each valve comprises a solenoid 68 and armature 70 attached to a valve closure plate 72. The latter closes off an opening 74 in a valve seat 76 and sealing means 78 is preferably provided to ensure a good seal. When plate 72 is lifted by the armature to the closed position shown in Figure 11 (a) gases below the plate 72 cannot exit via apertures between pillars 80.

De-energising the coil 68 causes the plate to drop to the open position as shown in Figure 11 (b) to permit gases to escape as shown by arrow 82.

In Figures 12(a) and 12(b), circulation around the treatment chamber 54 is denoted by arrows 84 and 86. A duct 88 at the front end of the chamber communicates with the underside of the straw (not shown in Figure 12) and the left hand valve 66'. When the latter is open, air and ammonia from the upper end of the duct 88 can exit the chamber. Fresh air is drawn in via the open valve 66" at the other, rear end of the chamber.

In use, straw to be treated is loaded into chamber 54 and the latter sealed shut. Ammonia from a liquefied source is supplied to expansion tank 10 where it expands and vapourises. The ammonia passes to unit 30 where it is mixed with air drawn from chamber 54 via outlet 62 and the mixture heated. The mixture is recirculated by the action of fan 44 through chamber 54 and unit 30 for an appropriate initial treatment time, typically about 1 6 hours. The temperature of the mixture is regulated by a thermostat (not shown) located in chamber 54 to control the heating by heating elements 32. The initial treatment is followed by a final treatment period in which fresh air is circulated through chamber 54 via valves 66 in order to clear the chamber of ammonia vapour.

The final treatment period is typically of the order of 4 hours, giving a total treatment time of about 20 hours. A control panel (not shown) serves to provide electrical output signals at timed intervals to control the overall process, including operation of valves 66 and other components.

Claims (11)

1. Apparatus for treating straw, comprising a sealable chamber for receiving straw to be treated, means for maintaining an ammonia laden atmosphere in the sealed chamber, means for treating the ammonia laden atmosphere in the sealed chamber, and an expansion tank external of the chamber for receiving liquid ammonia under pressure and wherein ammonia expands and boils prior to passage to the chamber, the expansion tank being provided with a series of internal baffles.

2. Apparatus according to claim 1, wherein the baffles in the expansion tank comprise a series of inclined plates vertically spaced above one another.

3. Apparatus according to claim 2, wherein respective drip trays are provided below the baffles for directing any liquid flowing off a particular baffle to the baffle beneath.

4. Apparatus according to any one of claims 1 to 3, wherein the expansion tank comprises heat exchanger fins.

5. Apparatus according to any one of the preceding claims, wherein an electrical heating element is provided for the expansion tank.

6. Apparatus according to any one of the preceding claims, wherein the expansion tank comprises an apertured spray bar for distributing liquid ammonia within the tank.

7. Apparatus according to any one of the preceding claims, including means for circulating heated air/ammonia mixture through the chamber and a heater unit.

8. Apparatus according to claim 7, wherein a fan and heater unit is associated with the chamber with an inlet and outlet communicating respectively with an outlet and inlet of the chamber for gas circulation, the unit also including an inlet for receiving ammonia gas from the expansion tank.

9. Apparatus according to claim 8, wherein the fan and heater unit is mounted to a rear wall of the chamber.

10. Apparatus according to claim 7, 8 or 9, wherein the heater is thermostatically controlled to regulate the temperature inside the chamber.

11. Apparatus according to any one of the preceding claims, wherein the floor of the chamber comprises steel ribs on which straw may be laid.

1 2. Apparatus according to any one of the preceding claims, wherein the chamber includes two solenoid valves for circulating fresh air through the chamber.

1 3. Apparatus for treating straw, substantially as herein described with reference to, and as shown in, the accompanying drawings.