WO2020058865A1

WO2020058865A1 - Process for treatment of organic waste from tanning cycle

Info

Publication number: WO2020058865A1
Application number: PCT/IB2019/057848
Authority: WO
Inventors: Massimo Neresini; Manuel ASNICAR; Marco Piva
Original assignee: Sicit Chemitech S.P.A.
Priority date: 2018-09-19
Filing date: 2019-09-18
Publication date: 2020-03-26

Abstract

The invention relates to a process of homogenisation of solid waste originating from the leather industry, followed by thermal pre-treatment which provides a material with excellent characteristics for feeding into an oxidation or reduction thermal decomposition plant.

Description

PROCESS FOR TREATMENT OF ORGANIC WASTE FROM TANNING CYCLE

The invention relates to a process of homogenisation of solid waste originating from the leather industry, followed by thermal pre-treatment which provides a material with excellent characteristics for feeding into an oxidation or reduction heat treatment plant.

The material obtained by the process according to the invention, hereinafter called “CARBORG”, consists of a mixture of waste with a high organic content also containing heavy metals, which is easy to handle, contains no foreign bodies, and is suitable for feeding into a heat treatment plant.

The invention also relates to a process for the treatment of solid waste originating from the tanning industry, which comprises feeding CARBORG into a pyrolysis/gasification or incineration plant.

Prior art

Disposal of solid waste with an organic matrix is becoming more and more complex because of stringent regulations and the increasing number of requirements which must be met before they can be sent to landfill. The high heat value of said products justifies their combustion with heat recovery in suitable plants, but the wide variety of their sizes and compositions, the presence of foreign bodies and handling difficulties can make it difficult or even impossible to design a waste-to-energy plant. Processes for converting leather manufacturing waste to fuel have been proposed. See, for example, CN101504143 and CN101724483.

Current treatment cycles for centralised water used in local tanning clusters involve operations which are very onerous in environmental terms, especially as regards the production of treatment sludge.

Over the years, in an attempt of reduce the quantity and improve the quality of this sludge, a gradual but inexorable reduction in the heat value of said wastewater has been observed (reduction in organic substance). US 1,963,909 discloses a heat treatment process for tanning waste, but starting with different raw materials and having different purposes from those of the present invention; the process described is useful to prepare a fertiliser, not a material intended to undergo heat treatment. US 2013/0248767 discloses a process for obtaining syngas from biomasses of plant origin which pose very different technical problems from tanning waste.

Description of the invention

An economical process for preparing fuels from waste with an organic matrix originating from the tanning cycle has now been found.

The invention involves the recovery of waste with a high heat value to be combined with wastewater treatment sludge so as to optimise heat and energy recovery.

The invention involves collection of the material, treatment under temperature and pressure conditions suitable for its transformation to a viscous, sticky fluid, and mixing of said fluid with sludge of low heat value, in amounts ranging between 50% and 150% by weight of the waste to be treated, to produce a material with a form, composition and energy content able to be recovered efficiently in a suitable treatment plant (reducing treatment, syngas formation and subsequent combustion with energy production).

The residue can optionally be stabilised with silicates (5 to 10% by weight of the material input into the heat treatment plant, depending on the alkaline earth content). In any event the amorphous final matrix immobilises the heavy metals present, thus rendering the residual solid material inert. The amount and volume of the residue are drastically reduced compared with the starting raw material.

The invention makes the plant energy self-sufficient, and also allows the recovery of other types of waste with the same favourable economic and environmental aspects.

In particular, the process according to the invention comprises:

a. sieving and grinding of waste;

b. treatment of the sieved, ground waste with direct steam at temperatures ranging between 120 and 170°C and pressure ranging between 6 and 8 bars; c. mixing of the viscous fluid obtained in step b with civil or industrial wastewater treatment sludge;

d. drying of the mixture and pyrolysis/ gasification treatment or incineration.

The various types of waste with an organic matrix originating from the tanning cycle are collected in a suitably equipped depot and loaded into a series of grinders and sieves to remove any foreign bodies that may be present.

The tanning waste that can be used in the process according to the invention comprises:

Buffing waste, coloured and uncoloured

Shavings, wet blue and wet white

Trimmings, wet blue and wet white

Coloured trimmings

Unsuitable hides

Whole hides

Hair and other types of reusable waste.

Said types of waste, when treated by the process according to the invention, add heat value to civil and industrial waste treatment sludge, leading to financial advantages in the disposal operation.

Dirty wooden pallets from factories, plastic packaging of chemical products, used plastic drums and used plastic tanks can also be employed, especially if they were used in the tanning industry.

After sieving and grinding the waste is mixed in closed systems, and direct steam is introduced until a temperature of 150°C and a pressure of 6-8 bars are reached. Either the continuous or the batch processing system can be used, and the average contact time is about 30 minutes.

The product discharged after treatment is a highly viscous liquid.

After heat treatment the product is mixed with sludge and other types of waste with a low content of organic substances which are difficult to treat, such as civil and/or industrial wastewater treatment sludge.

Said liquid is dried (fluid bed, flash dryer, low-temperature drying and the like). The dried product is then broken up into clumps and conveyed to a heat treatment plant.

The treatment plant generates waste with a“vitreous” matrix and practically zero release due to the addition of silicates.

This step can be performed in a reducing environment (pyrolysis/gasification) or an oxidising environment (incineration), the former being preferred due to its greater simplicity in the purification of effluent gases.

The crucial parameter of the destruction process is the temperature which, to guarantee the total breakdown of the waste, must exceed 1,100°C for a sufficient time, and in any event longer than 2 seconds (as specified in European Directive 2010/75/EU, art. 50, regarding incineration and co-incineration).

The destruction system in a reducing environment (pyroly sis/ gasification) involves the use of plasma torches as energy source. The plasma-producing gas can be air, oxygen-emiched air, an inert gas such as nitrogen, or argon.

The stream of a concentrated suspension of the product is injected into and nebulised in the plasma stream, which has a temperature exceeding 3000°C. In this way the water immediately evaporates. Moreover, due to the controlled injection of air for the purpose of partial oxidation of the organic substance, while keeping the reaction environment in reducing conditions, the temperature of the gas stream is maintained for a sufficient time at about l250°C, so that all the organic molecules break down into elementary, mainly inorganic molecules (H₂, CO, C0₂), with small fractions of short-chain hydrocarbons (CH₄, C₂H₆, C₂H₄, C₂H₂, etc.). Under these conditions, the organic fluorine produces hydrofluoric acid.

The gas is cooled by heat recovery and then purified in a wet scrubber (a Venturi scrubber or the like) operating with an alkaline solution, so that any acid gases present, such as hydrofluoric acid, are removed in the form of saline solution. The saline water, after filtration, is disposed of as wastewater. A final dedusting system, for example with a wet electrostatic filter, enables a combustible gas usable for energy recovery to be obtained. In particular, the water vapour necessary for the operation of the other sections of the integrated process can be produced.

The process according to the invention, in a typical embodiment thereof, converts 10-15 tons/day of buffing waste (5%), 30-40 tons/day of wet white shavings (12%), 20-30 tons/day of coloured trimmings (10%) and 220 tons/day of wet blue shavings (73%) to CARBORG by treatment at 160°C for 30 min. at 16 bars in the presence of 15 tons/day of water.

Figure 1 is a flow chart showing the treatment of 150 tons/day of organic waste by a local tanning cluster. The CARBORG can then be mixed with wastewater treatment sludge in weight ratios ranging between 50% and 150% of the input waste (e.g. in the ratio of 0.5: 1 relative to the dried sludge from wastewater treatment).

The destruction system in an oxidising environment (incinerator) uses combustion of an external fuel (usually natural gas) to maintain the desired temperature conditions in the combustion chamber (T>1100°C).

Fuel combustion takes place in an industrial burner; the aqueous suspension is nebulised in the combustion chamber.

Due to the high temperature, the organic molecules are completely dissociated. Acid gases (such as hydrochloric acid and hydro sulphuric acid), heavy metal salts and powders may be present in the effluent gases, depending on the aqueous suspension fed into the incinerator.

The effluent gases are then dedusted with a suitable system (such as ceramic filters) and undergo heat recovery in a suitable regenerator.

In particular, the water vapour necessary for the operation of the other sections of the integrated process can be produced.

Before expulsion into the atmosphere, the effluent gases are purified in a wet scrubber (a Venturi scrubber or the like) operating with an alkaline solution to remove acid gases. The saline water, after filtration, is disposed of as wastewater.

The systems can also be suitably combined so that other solid waste and other liquid waste can then be treated simultaneously.

Solid waste containing heavy metals such as chromium is preferably added at the reducing stage, producing a gaseous waste that can be conveyed to the subsequent oxidative stage, whereas liquid waste can be dispersed at the oxidative stage to produce energy, which is recovered in a“cogeneration” system that produces electricity and steam as a thermal energy vector.

The plants used in these stages can be small, and therefore suitable for small local facilities wishing to solve their own wastewater problem, or large, possibly also using internal heat recovery systems, electricity and steam cogeneration systems, and integrated water treatment and recirculation systems.

An indicative analysis of a sample typical of the product obtained by the process according to the invention is set out below:

The process according to the invention is advantageous because it significantly reduces the weight and volume of the solid waste originating from the tanning cycle.

The weight reduction is 70-80% and the volume reduction can be as much as 90% (the apparent density of the material increases from 0.6 Kg/L to about 2 Kg/L). Moreover, the heavy metals present are embedded in a vitreous matrix with practically zero release, thus eliminating the problem of pollutant residues and enabling the resulting solid waste to be reused as a by-product, for example as a roadbed filler.

The invention is described in greater detail in the examples below.

Example 1. Laboratory test

A mixture of tanning waste consisting of 2.5 Kg of wet white shavings, 1.25 Kg of buffing waste and 1.25 Kg of coloured trimmings (cut to a diameter of about 2 cm) is placed in a 10-litre steel reactor to which 2 litres of water are added. The reactor is closed and the mixture is heated to l60°C for about 30 minutes. The mixture is then cooled, discharged and dried.

Example 2. Drying pilot tests

A mixture of organic waste consisting of 25 Kg of wet white shavings, 12.5 Kg of buffing waste and 12.5 Kg of coloured trimmings (cut to a diameter of about 2 cm) is introduced into a 120-litre steel reactor to which 20 litres of water are added. The reactor is closed and the mixture is heated to 150°C for about 2 hours under stirring.

The mixture is discharged, and 25 Kg of dried sludge from a waste treatment plant is added. The resulting mixture is dried in a drying cabinet. The Carborg thus formed is sent for pyrolysis and gasification pilot tests.

Example 3. Gasification pilot tests

A mixture of organic waste consisting of 9.0 tons of wet white shavings, 4.0 tons of buffing waste, 4.0 tons of coloured trimmings, 2.0 tons of wet blue trimmings and 0.6 tons of wet blue shavings is divided into 10 loads and introduced into a 200-litre steel reactor to which 20 litres of water per load are added.

The reactor is closed and the mixture is heated to 150°C for about 2 hours under stirring.

The mixture is discharged and mixed with 12.0 tons of dried sludge from a waste treatment plant containing 85% dry matter, also divided into 10 loads.

The mixture is then dried in a continuous paddle-dryer using steam at 8 bars as thermal fluid.

The dried material, which has a granular appearance, is sent for gasification pilot tests.

The gasification pilot plant, which operates continuously with a discontinuous load of the material to be treated, is fed with 250 kg/h of dried material in loads of about 25 kg at about 6 minute intervals. 5 kg/h of coke and 15 kg/h of feldspar ore (a source of silicon) are loaded simultaneously.

The gasification plant produces about 70 kg/h of inert vitrified material which is left to solidify in crucibles, and about 800 N Vh of syngas, which is continuously analysed and burned in a torch.

Claims

1. A process for the preparation of combustible materials from organic matrix waste deriving from the tanning cycle, which comprises:

a. sieving and grinding waste;

b. treating the sieved, ground waste with direct steam at temperatures ranging from 120 to 170°C and pressures ranging from 6 to 8 bars;

c. mixing the viscous fluid obtained in step b with civil or industrial wastewater treatment sludge;

d drying the mixture and pyrolysis/gasification treatment or incineration.

2. The process according to claim 1 , wherein the waste comprises coloured and uncoloured buffing waste, wet blue and wet white shavings, wet blue and wet white trimmings, coloured trimmings, unsuitable hides, whole hides, hair and reusable waste.

3. The process according to claim 1 or 2, wherein the direct steam treatment is earned out for an average contact time of 30 minutes.

4. The process according to claim 1, wherein drying is carried out in a fluid bed or flash dryer, or by low-temperature drying.

5. The process according to claim 1, wherein the pyrolysis or incineration is canned out at temperatures above 1 l00°C for a time longer than 2 seconds.