Patent Application
20190000131
The present disclosure relates to a heater which may be used for curing tobacco or for another similar process, such as drying various plant materials.
The post-harvest processing of tobacco leaves usually includes a step of curing to remove moisture from the tobacco leaves and to achieve desired attributes of sensorial quality. As part of the curing process, the tobacco leaves are typically located on (or suspended from) racks in a barn. Included in the barn is a heating compartment, which includes a fan, heat exchanger and a furnace. The fan is used to move air from the barn into the heating compartment, where the air is heated by the furnace and heat exchanger, and then returned into the main area of the barn. An example of such a barn use for tobacco curing is disclosed in BR 8201451A.
In such a system, hot air (typically ranging from 30-80° C.) from the furnace leaves the heating compartment and enters the barn. In the barn, the hot air causes moisture to evaporate from the tobacco leaves, as part of the curing process, whereby the air is cooled somewhat by the evaporated moisture. The cooled air is then drawn back into the heating compartment to be re-heated by the furnace.
The air is therefore re-circulated between the heating compartment and the barn housing the tobacco to be cured. This re-circulation helps to improve the efficiency of the curing process, since the cooled air returning from the barn into the heating compartment is still generally warmer than the ambient (external) air temperature. Accordingly, it requires less input of energy to heat the re-circulated air to the desired temperature for curing than it would to heat external air to this temperature.
In many implementations, the furnace uses wood burning as its fuel source. In such a system (and also for other types of furnace), it is important to ensure that the recirculating air is not contaminated by smoke arising from the combustion of wood in the furnace, since such contamination could potentially impact the curing of the tobacco.
The disclosure is defined in the appended claims.
Some embodiments provide a heater for use in curing tobacco or other similar process, the heater comprising: a furnace having a chamber in which to burn fuel to generate heat; and a heat exchanger for transferring heat from the heater to an airflow for use in curing the tobacco or other similar process. The airflow passes outside the heater. The heat exchanger has one or more pipes that connect into the chamber of the furnace and is integrated into the furnace.
Some embodiments provide a heater for use in curing tobacco or other similar process. The heater comprises a furnace having a chamber in which to burn fuel to generate heat; and a heat exchanger for transferring heat from the heater to an airflow for use in curing the tobacco or other similar process, wherein the airflow passes outside the heater. The heat exchanger has a plurality of pipes that connect into the chamber of the furnace, wherein the plurality of pipes comprises two rows of pipes, one on each side of the furnace. The heat exchanger further including a plenum, wherein each of the pipes leads upwards from the furnace chamber to the plenum.
The heat exchanger may be integrated into the furnace by the use of one or more welded junctions or any other alternative sealing methods or materials. Sealing the junction or joints in the heater (e.g. body of the furnace, plenum, exchanger junctions, pipe walls, etc.) helps to prevent smoke leakage.
Various embodiments of the invention will now be described in detail by way of example only with reference to the following drawings:
In operation, the fan 150 is used to re-circulate air within the barn 100. In particular, the fan pushes air within the heating compartment 130 towards and past the heater 160, as indicated by arrow A, such that heat is transferred from the heater to the airflow. This produces a heated airflow which travels through a suitable opening 141C in a lower portion of the dividing wall 140 into the lower portion of the drying chamber 120, as indicated by arrow B. The heated air now rises and percolates through the racks of tobacco 122A, 122B and 122C, as indicated by arrows C (shown in broken line to indicate that this airflow may be intermingled with the racks of tobacco 122A, 122B and 122C). This procedure causes the airflow represented by arrows C to draw out moisture from the tobacco, which results in a slight cooling of the airflow, plus a drying of the tobacco.
Once the airflow has reached the upper portion of the drying chamber 120, the airflow travels back into the heating compartment 130 through a suitable opening 141B in an upper portion of the dividing wall 140, as indicated by arrow D. The airflow is then drawn into the fan 150, as indicated by arrow E, and another cycle then starts as the air re-circulates within barn 100.
It will be appreciated that
In addition, the barn 100 may also have the ability to vent a portion of the re-circulating air if the moisture content within the air becomes very high (or saturated), since this makes the air less effective at drawing moisture out from the tobacco leaves. As hot, very moist, air is vented out of the barn 100, cooler, less moist air may be drawn into the barn as a replacement. This newly introduced air then has to be heated up to the operating temperature of the interior of the barn for curing the tobacco leaves. (Note that for simplicity, the outlet to vent air out of barn 100 and the inlet to introduce external air into the barn 100 are omitted from
The heater 160 of
As shown in
The furnace includes a chamber 211 in which fuel, e.g. wood, is combusted to produce heat. The chamber has a generally cylindrical shape, where the central axis of the cylindrical shape lies approximately horizontal. At one end of the chamber (referred to herein as the front), as determined in a direction parallel to the central axis of the cylindrical shape, is a door 215. This door can be opened to allow fuel to be entered into the chamber 211.
The residue, e.g. ash, of fuel which is burnt in the chamber 211 falls into an ashtray 216 located underneath the furnace chamber 211. The ashtray also has a generally cylindrical shape, where the central axis of the cylindrical shape of the ashtray lies approximately horizontal, substantially parallel to the cylindrical axis of the chamber 211. The length of the ashtray (as measured along the cylindrical axis) corresponds approximately to the length of the chamber (also as measured along the cylindrical axis), in other words, the chamber and the ashtray are approximately co-extensive with one another.
The ashtray 216 is provided with a door 218 which can be used for removing ash from the ashtray. This door 218 of the ashtray is located approximately underneath the door 215 to the chamber 211. This configuration allows for easier access and configuration—e.g., ensuring that the heater 160 can be accessed from the front allows both fuel to be entered into the chamber 211 via door 215, and also ash to be removed from the ashtray 216 via door 218.
The legs 270 support the chamber 211 such that the ash-tray 216 is held on or above the floor of the barn. The latter arrangement may be helpful, for example, to allow enhanced air circulation around the heater, and also to prevent the ashtray 216, when hot, from over-heating the floor of the barn.
The heat exchanger includes two rows of pipes, 220A-1, 220A-2, 220A-3 and 220B-1, 220B-2, etc., one row on each side of the heater 160, and a hot air plenum 230. The hot air plenum has a configuration approximately in the form of an “H” arranged horizontally and is formed of two parallel (opposing) arms 231A, 231B joined by a cross-piece 232, where the arms extend in a direction parallel to the main cylindrical axis of the heater 160. The pipes in both rows are uniformly sized and shaped, with a substantially circular cross-section.
Each row of pipes 220A, 220B extends upwards from the chamber 211 to a respective arm 231A, 231B of the plenum 230. In this way, the pipes provide a path for hot air to rise out of the furnace 210 and pass into the plenum 230. There is one row of pipes on each side of the furnace 210, and each row extends outwards (i.e. away from the other row and from the centre of the heater) at an angle of approximately 30 degrees to the vertical. Within each row 220A, 220B, the pipes are horizontally spaced, in a direction substantially parallel to the main cylindrical axis of the heater 160.
The spacing between successive pipes, e.g. 220A-1, 220A-2, in a row is approximately equal to the width (diameter) of an individual pipe, so that the upper surface of a row of pipes, in the plane defined by the pipes themselves, has approximately equal portions of (i) the pipes themselves, and (ii) the spacings or gaps between the pipes.
Heated gases are able to leave the plenum 230 via an exhaust tube 250, which forms in effect an extension of the cross-piece 232 that bridges the two arms 231A, 231B of the plenum. In the implementation of
As an approximate indication of scale, the heater 160 has a total height of approximately 1.5 m, comprising approximately 0.35 m for the ashtray 216, 0.35 m for the plenum 230, and 0.8 m for the furnace 210. Each row of pipes 220A, 220B comprises 7 pipes, each of diameter approximately 0.1 m. However, it will be appreciated that these dimensions are indicative only, and will vary from one implementation to another, depending upon the size of the barn for heating, plus many other parameters.
The ashtray is also provided with a small fan that connects to a pipe which leads outside the barn (this small fan and pipe are omitted for simplicity from the Figures). The fan draws in external air through the pipe, and this external air then passes firstly into the ashtray 216, and from there into the furnace chamber 211. Note that there is relatively little risk of leaking combustion products via this air inlet, since this would require the leaking gas to flow against the pressure differential (and incoming air stream) created by the fan.
In operation, the gaseous/vapour combustion products (and hot air) from the furnace pass up through the pipes 220 into the plenum, and from there into the exhaust 250. More particularly, the exhaust, like the air inlet into the ashtray, is connected via a pipe, chimney, or some other form of vent (not shown in the Figures) to the outside of the barn, hence the hot gas and vapours are vented outside rather than into the interior of the barn. Note that the location of the exhaust vent should be at a significant distance from any external air intake to provide air for recirculation within the barn (e.g. to replace air that has become saturated with moisture). One way of helping to achieve this is to have the exhaust pipe 250 connected to a chimney of sufficient height that the exhaust gases are dispersed or dissipated over a very wide area (and away from any air inlet).
The air used for curing the tobacco generally re-circulates within the interior of the barn, as indicated by arrows A, B, C, D and E in
It will be appreciated that the heat exchanger, in particular the rows 220A, 220B of pipes, is configured to help the efficiency of this heat transfer. For example, the sloping angle of the pipes 220 (i.e. away from the vertical) provides a high surface area target for the re-circulating air as it is pushed downwards by the re-circulating fan 150, as indicated by arrow A in
The heater 160 of
For a typical barn arrangement, for example as illustrated in the above-mentioned patent BR8201451A, the heater 160 is located in a front area of the barn 100, in the substantially the same location as the ventilation system, i.e. fan 150. In particular, the heater 160 is sited just below the ventilator 150. This helps to concentrate body of the furnace 210 and the pipes 220 of the heat exchanger in a region where the air flow maximizes heat transfer. This configuration is supported by a uniform distribution of the pipes in each row of pipes 220A, 220B, which helps to ensure an even gas flow in the heat exchanger (and hence a more even heating of the airflow past the heat exchanger).
As noted above, in barns that use firewood fuel for curing tobacco, there is a risk of smoke leaking into the barn through cracks or holes in the pipes or furnace, or through incorrect installation of pipes. Such leakage may potentially contaminate the tobacco leaves, which can decreases leaf quality in the barn, and may also interfere with sensory attributes of the tobacco, and so represents a loss of some of the qualitative characteristics of the tobacco. However, the heater 160 described herein has a one-piece (integrated) design that provides a furnace 210 which is joined to (integrated with) the heat exchanger by means of welded junctions. Such a construction helps to minimise the chance of leaks from connections between the furnace and the heat exchanger. Accordingly, the heater 160 offers an effective way to improve tobacco quality, whilst retaining the ability to use an energy resource (firewood) which is currently adopted in a considerable number of countries.
As described herein, the heater 160 acts as a gas-to-gas heat exchanger linked to the furnace 210. The heat exchanger is located above the furnace and includes two sets or rows of pipes 220A, 220B, one on each side of the furnace 210. Both sets of pipes are connected to the hot air plenum 230, which in turn leads to an exhaust facility 250.
Having the pipes 220A, 220B arranged in an inclined manner, i.e. between horizontal and vertical, helps heated gas to rise out of the furnace 210 through the pipes 220A, 200B and into the plenum, while at the same time offering a good surface area for heat transfer to air which flows around the heater 160. In addition, the inclined orientation of the pipes 220A, 220B also helps to prevent ash deposit in the pipes. This configuration of furnace and heater is formed with welded joints, e.g. between the pipes 220 and the heating chamber 211 and the plenum 230 to prevent the leakage of smoke. This helps to ensure that combustion products from the furnace 210 do not escape from the heater 160 into the re-circulating air within the barn drying compartment 120, since such leakage might potentially contaminate or degrade the tobacco during the curing process.
The inclined configuration of the pipes 220 is also arranged to help avoid ash deposit and to facilitate cleaning, as illustrated in
In order to facilitate active cleaning, the windows 235A and 235B at the front of respective arms 231A, 231B of the plenum 230 are removable, as shown in
Accordingly, front windows 235 allow both inspection and also easy cleaning. As shown in
While the construction and operation of heater 160 as described above can lead to reductions in contamination of the tobacco leaves in the barn 100, it is also sensible to complement these actions with other measures to help prevent the entry of smoke through a vent to the barn 100. Accordingly, appropriate filters may be installed into any such vents, ventilators, ducts or other air circulation systems involved in the curing barn 100 in order to further reduce any potential contamination.
A further factor in reducing any contamination is furnace management during the tobacco curing process. Thus opening the door 215 of the furnace chamber for re-stocking with fuel may potentially release smoke into the environment, which in turn may possibly get into the barn through the vents. The heater 160 can therefore be operated using an automatic stocking system (not shown in the Figures), which can help to reduce the number of times the furnace door 215 is opened during the curing process. Such an automatic stocking system again helps to reduce any smoke leakage, while also offering the possibility of improved fuel efficiency.
The heater described herein therefore provides an improved design for a combined furnace and heat exchanger that helps to offer, inter alia, an increase in the quality of the cured tobacco (less contamination), just one exhaust pipe for easy connection to a chimney or other external vent, and a reduction in firewood consumption. Furthermore, cleaning is facilitated because an inspection window provides full access to the interior of the heat exchanger, so that the pipes 220 and other components of the heat exchanger do not need to be disassembled for cleaning. In addition, the ash deposits in the heat exchanger are decreased by reducing the number of horizontal pipes; in particular, pipes 220 generally avoid ash deposits by virtue of their significant inclination away from the horizontal.
The heater 160 reduces the number of junctions between pipes compared to a conventional furnace and heat exchanger used in tobacco flue-curing barns. In particular, there are no (internal) connections to be made at installation between the furnace 210 and the heat exchanger (unlike for conventional systems), and the only external connection or junction for heater 160 is to connect the exhaust 250 to or through an external vent. (There may also be a connection for the air inlet into the ashtray, but as noted above, this has minimal risk of leakage, because it can be configured solely for flow into the heater 160).
In some implementations, the cross-bar 232 of the plenum may extend sufficiently to allow the exhaust pipe 250 (as welded to the heater 160) to pass into a separate compartment or room, or directly to an external vent. In this case, any junction or seal around the end of the exhaust pipe 250 may be located outside, and separated from, the recirculating airflow. Such a configuration may help to further reduce the risk of any leakage of combustion products into the recirculating airflow.
Although the above description has focussed on certain embodiments of the heater 160, the skilled person will be aware of various potential modifications, enhancements, simplifications, etc, according to the circumstances of any given implementation. For example, the configuration and connectivity of the plenum may be modified as appropriate (e.g. not necessarily an H-shape, different numbers and/or layout of pipes, etc). In addition, the furnace 210 might use a different heat (combustion) source rather than wood, such as liquid petroleum gas (LPG), coal, biomass, etc. In addition, the heater may include a different type of heat exchanger, for example, gas-to-liquid, depending upon how the heat is to be transferred from the furnace to the material to be heated. In addition, other techniques to help reduce or minimise smoke leakage may also be employed by the modification of the described heater 160 or applied to the conventional systems already commercially available, such as pipes junctions with flanges and clamps (e.g. for the exhaust 250), single continuous piece pipe (no junctions, e.g. original junctions welded) for heat exchanger and/or the use of sealing materials at such junctions, e.g. synthetic polymers as used in the vehicle industry.
The heater described herein can be used to dry or cure different plant parts and/or food (not just tobacco)—e.g. grains and tea. Furthermore, although heater 160 as described above is formed from metal with welded junctions, other implementations may also utilise (at least in part) other materials, such as brick or concrete. Furthermore, the welded junctions may be replaced (at least in part) with other junctions that provide an appropriate level of sealing, e.g. by using junctions between pipes and the furnace and/or the plenum, wherein the junctions are provided with flanges and/or clamps (etc.) to obtain the requisite level of sealing at the junctions.
In conclusion, in order to address various issues and advance the art, this disclosure shows by way of illustration various embodiments in which the claimed invention(s) may be practiced. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding and to teach the claimed invention(s). It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope of the claims. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc other than those specifically described herein. The disclosure may include other inventions not presently claimed, but which may be claimed in future.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1512343.3 | Jul 2015 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2016/051020 | 4/12/2016 | WO | 00 |
