GB2159274A - Method and apparatus for producing solutions - Google Patents

Abstract

A tank suitable for the batch production of relatively large quantities of solutions, such as liquid fertiliser, has a base wall 10, there being an indicator mounted centrally to upstand from that base wall. The indicator comprises a rigid pole 16 carrying three triangular markers 17, apex lowermost, one marker touching the base wall and the other two being spaced upwardly therefrom, their positions being determined by calculation or empirically. Liquid is run into the tank until the level reaches the middle marker, and then solid is added until the liquid level reaches the top marker, the solution thus being produced on a volumetric basis. If the tank is not completely empty, the level relative to the lowest marker is noted and the level is raised to corresponding positions of the middle and top markers. <IMAGE>

Description

SPECIFICATION Methods and apparatus for producing solutions This invention relates to a method of producing a solution of a required concentration, and also to apparatus specifically adapted for performing such a method.

When a solution of a solid material in a liquid is required, the solid material is commonly supplied in a granular or pulverulent form and a pre-determined mass of the material is added to a measured quantity of the liquid. Sometimes, it is more convenient to weigh out the material into a mixing container, and then to add a measure volume of liquid to that container.

Provided that the relative proportions of the volume of liquid and weight of solid have properly been pre-determined, such mixing methods may accurately and reliably result in a solution of the required concentration. However, when relatively large quantities are being mixed to produce a solution, the problems of accurately weighing the solid matter and of measuring the liquid volume may become acute, giving rise to significant deviations from the required solution concentration.

As an example of the foregoing, in the case of the mixing of liquid fertilizer for spraying over arable land, it is convenient for a farmer to produce the liquid fertilizer by dissolving a nitrogeneous compound in water, mixing in one batch a quantity for spraying. For instance, the farmer may wish to mix up to fifteen tonnes of solution, dissolving six tonnes of pulverulent or granulate nitrogeneous compound in nine tonnes of water. However, the problem of accurately weighing on a farm four tonnes of solid material is quite considerable, for few farmers have a weigh bridge. Whilst the solid material could be bagged by a distributor into small, handlable quantities, it obviously would be most expensive, as compared to the price of such materials in bulk. Moreover, the accurate measurement of six tonnes of water is not easy.

In an attempt to overcome the foregoing problem, it has been suggested that the appropriate quantities should be determined purely on a volumetric basis, by providing appropriate marks on the side wall of the tank in which mixing is to be performed. Water may then be added to the tank up to a first mark, whereafter the solid is tipped into the tank until the water level is at a second, higher level; on completion of the dissolving process, one would expect the concentration to be approximately correct, provided the marks were correctly positioned.

It will be appreciated that in order to mix fifteen tonnes of nitrogen fertilizer solution, the tank in which the mixing is performed must be of most considerable dimensions.

One known design of mixing tank for this purpose measures some sixteen feet long (about 4.8m), eight feet wide (about 2.4m) and four feet high (about 1.2m). Experiments with such a tank have shown that even if carefully positioned marks are provided on a side wall of such a tank, considerable errors in the resultant solution strength may arise owing to the tank being rested on a surface which is not truly horizontal. The errors may be reduced by providing the markings approximately midway along the long wall of the tank, rather than on an end wall thereof, but even so experiments have shown that the tank need not be greatly out of horizontal for errors in the concentration to rise to as much as 10%.Particularly in the case of liquid fertilizers, an error of this magnitude is not acceptable: if the strength is too high, growing plants may be damaged and in any event the cost of fertiiizing a given area will rise, whereas if the concentration is too weak, inadequate restoration of the nitrogen levels will be obtained, leading to poor plant growth.

It is an object of this invention to provide a method and apparatus permitting the accurate production of a solution at a required strength, particularly for relatively large batches of such solutions, such as of the order of fifteen tonnes of solution.

Accordingly, one aspect of this invention provides a method of producing a solution of a required concentration, comprising providing an upstanding indicator in the central region of a tank in which the solution is to be produced, pouring liquid into the tank until the liquid level reaches a first marker on the indicator, and then adding solid material into the tank until the liquid level reaches a second marker on the indicator.

It will be appreciated that in performing the method of this invention, the quantity of liquid and the quantity of solid required to make a solution of the required concentration are determined volumetrically, and that the required respective volumes are determined beforehand, either empirically or by calculation, so as to permit the provision of appropriate markers on the indicator. By arranging for the indicator to upstand from a central region of the tank, any errors resulting from the tank being out of level are greatly reduced, and will be mostly averaged out.In the case of a relatively large scale batch production process, such as has been mentioned above concerning the production of 1 5 tonnes of liquid nitrogen fertilizer, it can be demonstrated that a tank may be considerably out of level, and yet the errors in the required concentration still remain well within acceptable limits similar to those which would have been achieved had the tank been truly level.

It is preferred for each marker on the central indicator to extend vertically above the exact required level in such a manner that a user may estimate how much above the required level is the actual level. Then, by providing a similar third marker extending upwardly from the bottom of the tank, the method of this invention may be performed so that in the case where the tank is not completely empty at the commencement of the production of a batch of solution, initially an assessment of the liquid level in the tank is made against the third marker, then liquid is poured into the tank until the liquid level reaches a similar level with respect to the first marker on the indicator, and finally solid material is added until the liquid level reaches a similar level with respect to the second marker on the indicator.

Though each marker could simply carry convenient graduations, it is preferred for each marker to have a changing shape as considered in the vertical direction, so that an assessment of liquid level against that marker may be made by the apparent shape of the marker visible above the liquid level. For example, each marker may be of generally triangular shape, apex lowermost.

According to a second aspect of this invention, there is provided a tank for use in a batch process for producing a solution of a required concentration, which tank comprises a base wall and one or more upstanding peripheral side walls, the tank further comprising an indicator provided in the central region of the tank so as to upstand from the base, the indicator having at least two markers thereon spaced vertically the position of which markers is pre-determined such that pouring liquid into the tank to the first marker and then adding solid material until the liquid level reaches the second marker produces a solution of the required concentration.

Though the volumetric measurement errors are greatly reduced by arranging the indicator to upstand generally from the central region of the tank, the errors may be minimised by ensuring the indicator upstands from the exact geometric centre of the tank.

It is preferred for each marker to be of triangular shape when viewed from the side, attached to the indicator with its apex lowermost. Each marker could therefore be of conical or triangular pyramidal form, but it is preferred for each marker simply to comprise a flat plate of triangular shape. Such markers should be mounted so that the apex is at the required level for the liquid in order to produce the appropriate concentration of the final solution.

A third marker of similar form to the other two markers may also be provided, which third marker is mounted on the indicator with its apex in contact with the base of the tank.

At the commencement of a batch production process for solution, should any liquid remain in the tank from a previous batch, an assessment may first be made of the liquid level relative to the first marker, and then the levels of the liquid with respect to the first and second markers adjusted accordingly.

The solution producing tank of this invention may be of circular, rectangular, square or other shape in plan. It moreover may be provided with such other means as are appropriate in order to dissolve the solid material in the liquid. For example, the tank may be provided with one or more agitation devices, circulation pumps, heat exchangers and the like.

By way of example only, one specific embodiment of this invention will now be described in detail, reference being made to the accompanying drawing, which is a perspective view of a tank constructed and arranged in accordance with this invention.

The tank illustrated in the drawing is fabricated from steel by welding and comprises a base 10 of rectangular shape and four upstanding side walls 11, 12, 13 and 14.

Triangular reinforcing gussets 1 5 are provided as appropriate to impart sufficient strength to the tank. The tank is carried on five rails of Isection welded to the underside of the base 10 at appropriate intervals. Such a tank, suitable for use in the batch production of up to fifteen tonnes of a liquid nitrogen fertilizer may have dimensions of the order of: Length 4.8m Width 2.4m Height 1.2m Capacity (approximately) 1 3.8 x 103 litre.

Such â tank may conveniently be used for the production of approximately fifteen tonnes of liquid fertilizer solution, using nine tonnes of water and six tonnes of granulate urea.

Weided into the tank so as to upstand from the centre of the base 10 is a rigid pole 16, which pole carries three triangular markers 17, spaced apart along the length of the pole 1 6. Each marker comprises a flat plate of triangular shape, welded to the pole 1 6 at a pre-determined position, with its apex lowermost. Marker 1 7 has its apex touching the bottom of the tank, whereas markers 1 8 and 1 9 have their apices at predetermined positions above the base of the tank. For the tak of this invention, designed to-produce the solution discussed above, the apex of marker 1 8 is 750 mm above the base of the tank, whereas the apex of marker 1 9 is 1110 mm above the base 10.

In order to permit the tank described above to be used in the production of nitrogen fertilizer using water and urea, it is ncessary to provide an agitation device and also means arranged to permit heat to be imparted to the solution, in view of the fact that the dissolving of urea in water is endothermic. Such means are well known in the art and form no part of this invention; they will not therefore be de scribed in detail here.

To use the tank to produce a batch of a fertilizer, first of all an assessment of any remaining liquid level in the tank is made, against marker 1 7. This is done by observing the amount of the marker showing above the liquid level in the tankand of course if there is no liquid in the tank, the whole of the marker is visible. Then, water is poured into the tank until the level reaches a corresponding position against marker 18; if the tank was empty at the commencement of the process, water is added simply until it reaches the apex of marker 18. Urea granules are then tipped into the tank, until the liquid level reaches the corresponding position against marker 1 9-and again, if the tank was empty at commencement of the process, the urea is added until the level reaches the apex of that marker. Provided that the markers were accurately positioned beforehand, either from empirical or calculated data, when the solution has been completed by dissolving all of the urea in the water, it will be found that the concentration of the solution is well within acceptable limits even if the tank is lying on a surface which itself may be several percent out of level.

Claims (12)

1. A method of producing a solution of a required concentration, comprising providing an upstanding indicator in the central region of a tank in which the solution is to be produced, pouring liquid into the tank until the liquid level reaches a first marker on the indicator, and then adding solid material into the tank until the liquid level reaches a second marker on the indicator.

2. A method of producing a solution of a required concentration according to claim 1, in which each marker of the central indicator has a vertical extent above the required level to permit an estimation of the actual level above the required level.

3. A method of producing a solution of a required concentration according to claim 2, in which the central indicator is provided with a third marker extending upwardly from the bottom of the tank and also having a similar vertical extent to the other markers, in order that for a case where the tank is not completely empty at the commencement of the production of a batch of solution, initially an assessment of the liquid level in the tank may be made against the third marker, then liquid is poured into the tank until the liquid level reaches a similar level with respect to the first marker on the indicator, and finally solid material is added until the liquid level reaches a similar level with respect to the second marker on the indicator.

4. A method of producing a solution of a required concentration according to claim 2 or claim 3, in which each marker of the central indicator used carries vertical graduations.

5. A method of producing a solution of a required concentration according to claim 2 or claim 3, in which each marker of the central indicator used has a shape which varies in the vertical direction, so that an assessment of liquid level against that marker may be made by the apparent shape of the marker visible above the liquid level.

6. A method of producing a solution of a required concentration according to claim 5, in which each marker used is of a generally triangular shape, apex lowermost.

7. A method of producing a solution of a required concentration substantially as hereinbefore described with reference to the accompanying drawings.

8. A tank for use in a batch process of producing a solution of a required concentration, which tank comprises a base wall and one or more upstanding peripheral side walls, the tank further comprising an indicator provided in the central region of the tank so as to upstand from the base, the indicator having at least two markers thereon spaced vertically and the position of which markers is predetermined such that pouring liuid into the tank to the first marker and then adding solid material until the liquid level reaches the second marker produces a solution of the required concentration.

9. A tank according to claim 8, wherein a third marker similar to the other two markers is provided, which third marker is mounted on the indicator with its lower edge in contact with the base of the tank.

10. A tank according to claim 8 or claim 9, wherein each marker is of triangular shape when viewed from the side, attached to the indicator with its apex lowermost.

11. A tank according to claim 10, wherein each marker is of conical or triangular pyramidal form.

12. A tank according to claim 10, wherein each marker comprises a flat plate of triangular shape, mounted so that an apex is lowermost and at the required level for the liquid in order to produce the appropriate concentration of the final solution.

1 3. A tank according to any one of claims 8 to 12, wherein means are provided to facilitate the dissolution of added solid material into liquid previously run into the tank.