JP4031345B2 - Method for drying hydrous waste - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for effectively drying moisture from various hydrous wastes.
[0002]
[Prior art]
In order to reuse food waste, agricultural waste, fish / meat livestock residue, sludge and other water-containing waste as feed, fertilizer, etc. Drying is conventionally performed.
In drying, in order to prevent the generation of malodor and facilitate the treatment of the removed moisture, a vacuum dryer (vacuum dryer) is increasingly used.
[0003]
[Problems to be solved by the invention]
In order to increase the thermal efficiency, vacuum drying is usually performed while stirring the material to be dried, but it takes time to evaporate the water contained in the material to be dried, which increases the drying time and deteriorates the thermal efficiency. It was. In particular, if the material to be dried is agricultural / livestock waste, activated sludge, etc., it takes a long time for moisture contained in animal / plant cells and microbial cells to pass through the cell membrane, impairing the drying operation. It was.
Therefore, an object of the present invention is to provide a method capable of efficient drying even when the water-containing waste contains internal water such as microorganisms of animals, plants and activated sludge. is there.
[0004]
The evaporation rate of the external water is much faster in the external water around the solid content of the material to be dried and in the internal water contained in animals / plants or microorganisms.
This is because (1) the external water is outside the solid, so that the contact efficiency with the hot air for drying or the heat transfer surface is good. (2) The internal water is surrounded by the cell membrane, and the cell membrane is internal water. This is to inhibit the diffusion of.
[0005]
As a result of various studies to promote the drying of internal water, the present inventor first dried the object to be dried in the presence of an inorganic salt or an inorganic acid. As the water evaporates, the concentration of inorganic salt or acid increases and the osmotic pressure of the external water increases, and the internal water of plants and microorganisms moves to the external water side, thereby increasing the evaporation rate of the internal water. As a result, the present invention has been completed.
[0006]
[Means for Solving the Problems]
The above object is achieved by the present invention described below. That is, the present invention is a method for drying hydrous waste, which comprises drying hydrous waste containing animals, plants, or microorganisms using a vacuum dryer in the presence of an inorganic salt or an inorganic acid. The salt is any one selected from Na ₂ SO ₄ , NaNO ₃ , NaH ₂ PO ₄ , Na ₂ HPO ₄ , Na ₃ PO ₄ , CaCl ₂ , Ca (NO ₃ ) ₂ and MgCl ₂ , and the inorganic acid is phosphorus Sandea is, and, an inorganic salt or an inorganic acid, is a method for drying water-containing waste, characterized in Rukoto is present in the range of 0.01 to 10% by weight relative to the water content of the hydrous waste .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.
Examples of the water-containing waste targeted by the present invention include food residues such as okara, sake lees, used rice cakes such as tea and coffee, food waste from households and restaurants, etc .; fish and livestock waste; vegetable waste, Agricultural waste such as vegetable and fruit squeezed rice cakes; various sludges such as activated sludge; pressurized flotation scum; manure of livestock such as cattle, pigs and chickens; various concentrated waste liquids. The type of water-containing waste is not particularly limited, and the water content is not limited.
INDUSTRIAL APPLICABILITY The present invention is suitable for drying hydrous waste containing objects having internal water such as sludge containing animals / plant residues and microorganisms.
[0008]
The feature of the present invention is that an inorganic salt or an inorganic acid (mineral acid) is allowed to coexist when the water-containing waste as described above is dried to remove moisture.
Inorganic salt used in the present invention, an alkali metal or alkaline earth metal salts of inorganic acids (mineral acids) are preferred, for _{example, N a 2 SO 4, NaNO} 3, NaH 2 PO 4, Na 2 HPO 4, Na ₃ PO ₄ , CaCl ₂ , Ca (NO ₃ ) ₂ , MgCl _{2 and the} like. Examples of the inorganic acid (mineral acid), Ri include the I acid. It is desirable to select the inorganic salt or the inorganic acid in consideration of the reuse of the dried hydrous waste.
[0009]
When drying the water-containing waste, in the form hydrous waste (hydrous solid, slurry solids, liquids, etc.) dryers Ru is used in accordance with the. For example, aeration box dryer, aeration band dryer, rotary dryer (usually vacuum type, cylindrical dryer itself rotates. There are direct heating type and indirect heating type heating methods), spray drying Accelerate drying by agitating the material to be dried by rotation of a stirring blade provided in a machine (spray dryer), evaporator, or non-rotating cylindrical dryer (in the case of the indirect heating method, the dryer wall and the direct heating method) And a stirring type vacuum dryer that pulverizes the dried material to be dried together with a heating medium (usually water vapor or heated air). A preferable dryer in the present invention is the above-described agitation type vacuum dryer that is hermetically sealed and does not leak malodor to the outside, and can be easily removed by adsorption of malodor or the like and can be recovered and processed. By using a vacuum dryer and adjusting the degree of vacuum, for example, it is possible to dry the hydrated waste at a low temperature of about 50 ° C. The operating conditions of the vacuum dryer are not particularly limited, and can be set as appropriate according to the water content of the water-containing waste.
[0010]
When the water-containing waste is vacuum dried, the amount of inorganic salt or acid used is adjusted according to the water content of the water-containing waste. Usually, the inorganic salt or the inorganic acid is preferably used in an amount of 0.001 to 10% by weight, more preferably 0.01 to 10% by weight, based on the water content of the hydrous waste. If the water-containing waste contains animals / plants and microorganisms, or if solids that absorb moisture are contained inside, the above amount may be further increased by about 10 to 50% by weight. preferable.
Inorganic salts or inorganic acids can be added to hydrous wastes either by mixing and dissolving them in hydrous waste in advance and then putting them in a vacuum dryer, or by adding hydrous wastes in a vacuum dryer. A salt or an inorganic acid may be added and dissolved.
[0011]
By using a vacuum dryer, the recovered water can be reused by being treated as it is or if necessary, or discharged into a river. On the other hand, the dried powdery waste can be reused as feed or fertilizer depending on the type.
[0012]
【Example】
The present invention will be specifically described below with reference to examples and comparative examples.
[0013]
Example 1 and Comparative Example 1
The following hydrated waste was dried using a stirring type cylindrical vacuum dryer (actual volume: 0.33 m ³ , heat transfer area: 4.99 m ² , stirring power: 2.2 kw) whose schematic cross-sectional view is shown in FIG. .
200 kg of activated sludge cake having a water content of 83% by weight was put into a vacuum dryer, and then 0.5 kg of calcium chloride (CaCl ₂ ) (0.3% by weight with respect to moisture) was added to start drying. The film was dried for 6 hours under conditions of a degree of vacuum of 75 mmHg (10 kPa) and an internal temperature of 55 ° C. The dried waste was powdery and the water content was 4.8% by weight.
Further, the same water-containing waste as described above was dried under the same conditions except that calcium chloride was not used. The moisture content of the dry waste was 28% by weight and powdering was insufficient. The total drying time until reaching the same water content as above was 11 hours.
[0014]
Example 2 and Comparative Example 2
Using the same vacuum dryer as in Example 1, 120 kg of vegetable scrap having a moisture content of 96% by weight was added, and then 0.3 kg of phosphoric acid (0.27% by weight with respect to moisture) was added. It was dried for 6 hours under the same conditions as in Example 1. The dry waste produced by the method of the present invention was powdery and had a moisture content of 8.2% by weight. On the other hand, the dry waste of the comparative example had a moisture content of 33% by weight, and the total drying time until reaching the same moisture content as above was 13 hours.
[0015]
【The invention's effect】
According to the present invention described above, drying of hydrous waste, which can be efficiently dried and dried waste can be recycled even when the hydrous waste contains plants or microorganisms having internal water. A method is provided.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an example of a stirring type vacuum dryer used in the present invention.

Claims (2)

A method for drying water-containing waste comprising drying a water-containing waste containing animals, plants, or microorganisms in the presence of an inorganic salt or an inorganic acid using a vacuum dryer, wherein the inorganic salt is Na ₂ SO _{4, NaNO 3, NaH 2 PO} 4, Na 2 HPO 4, Na 3 PO 4, CaCl 2, Ca (NO 3) is any one selected from ₂ and MgCl _2, and inorganic acids Ri phosphate der, and , method of drying an inorganic salt or an inorganic acid, water waste, wherein Rukoto is present in the range of 0.01 to 10% by weight relative to the water content of the hydrous waste.   The method for drying hydrous waste according to claim 1, wherein the hydrous waste is food residue, agricultural waste, fish / livestock waste, livestock manure, or sludge.

Images