Description:FIELD OF THE INVENTION
The present invention relates to the development of a cleaning system and a method for cleaning the clogged material from the filter clothes of the filter press. Specifically, it relates to a set-up involving an acid treatment followed by high pressure water washing of the cloth over a specially designed set-up. The present invention thus provide a process of cleaning clogged filter cloth of filter press and a system set-up for cleaning of choked filter cloth subsequent to its dewatering of slurry. The cleaning of the filter cloth is accomplished with a set of chemical and physical means to separate the embedded solid particles from the filter pores, after dewatering a slurry. The filter cloth is effectively cleaned with acid solution, where the cloth is soaked in 25 to 50% dilutedcitric acid solution that do not generate any fumes.The filter is further subjected to 80 to 120 bar water pressure for cleaning. These cleaned filters are then kept soaked in water tillnext use.

BACKGROUND OF THE INVENTION
Ultra fine particulates of iron ore are used in a beneficiation plant for the manufacture of Iron ore pellets that are charged in iron production units such as Blast furnace or DRI or Corex process. The ultra-fine particulate of iron ore is made into a slurry with water at ore to water ratio of 1:8. This slurry is generated by wet grinding of water in ball mills. The slurry from the process is subjected to dewatering of the slurry in a filtration unit. The dewatered fines are suitable for agglomeration to make iron ore pellets.

The filtration unit typically consist of 12 filters in it and each filter consists of 120 filter clothes. The iron ore slurry is loaded on each filter cloth and the slurry is dewatered at a speed of 1.8 to 1.9 ton per minute. The full capacity of a filter press is 28 tons and the loading dewatering cycle takes place within 15 min duration. The dewatering is done by squeezing the slurry contained in the filter cloth by hydraulic cylinders. After dewatering, the hydraulic cylinder is removed and a green iron ore cake with about 9 to 10% of moisture is obtained. The wet cake is transferred through a conveyor system for drying and crushing, where this material converted into dry ultra-fine iron oxide.

During filtering the fine particulates clog the filter clothes and brings down the efficiency of filtration. Hence, after every high pressure dewatering of the filter cloth, it has to be properly cleaned free of material clogged in the pores of the filter, so that it can be efficiently used for the next cycle.

In a beneficiation plant, the iron ore is liberated from gangue by comminution using crushers followed by enrichment of iron by screening. This is followed by wet grinding the enriched ore in a ball mill water media to further liberation is a slurry media followed by further concentration of the iron ore mineral. The iron ore slurry from the wet grinding and beneficiation units carries ultra fine iron ore particulate in a water slurry. The iron value enriched iron ore slurry, is usually dewatered and dried to get iron ore cake that can be dried and pelletized into iron ore pellets for its conversion to iron, in iron making plants.

The dewatering of the iron ore from the slurry is carried out using different types of filter presses and Plate type filter press is the most common technique. The filter presses have filter clothes which selectively allow water from the slurry to be filtered by pressing the solid iron oxide accumulated on the filter cloth. The slurry is squeezed against the filter cloth to ensure proper high pressure solid liquid separation. The filter cloth is made of Polypropylene high tensile strength which withstands high pressures. During filtering, the fine slurry particles, pass through the filter mesh, till a layer of dewatered solids accumulates on the cloth surface. The accumulated solids then begin to filter additional slurry material, capturing virtually all the solid particles and allowing only clear liquid (filtrate) to pass through the pores in the filter cloth.

The initial filtering of the slurry material will cause choking of the filter cloth over an extended period of usage of the filter. The cloth surface undergoes normal wear, when the cakes are discharged from the filter press at the end of the dewatering cycle. The wear of the filter cloth is very much dependent on the abrasive characteristics of the iron ore cake material and the wear resistance of the cloth material. It is difficult to predict, the normal cloth life cycle for any Filter Press application, but a good quality cloth material should last for hundreds, if not, thousands of cycles.The Iron ore slurry is a very soft and sticky in nature, causing choking of filters rather than greatly causing wear or damages. The choking of the filter clothes affects, the efficiency of filter and may compromise with the throughput of the material.

The behaviour of filter clothes in a hydraulic press system result in dewatering of iron ore slurry at high pressure. It has a very high ability to lower the water content in a slurry. The filter clothes have a drawback that repetitive operational cycles cause clogging of its filter cloth, which in turn drops filtration efficiency noticeably and is finally dumped.

The present filter clothes in operation,is made of Polypropylene material and is resistant to acid attack when the filter cloth is cleaned by environmentally compatible aliphatic organic acid such as citric acid. The polypropylene fibre has a high tolerance for both acidic and alkali cleaning solution.

When polypropylene cloth is treated with water, the water can act as a plasticizer, meaning it can reduce the glass transition temperature (Tg) of the polypropylene. The glass transition temperature is the temperature at which an amorphous polymer, like polypropylene, transitions from a rigid, glassy state to a more flexible, rubbery state.When the Tg of polypropylene is lowered due to water treatment, the polymer chains become more mobile and are more likely to move and rearrange themselves. This can lead to a reduction in the material's dimensions, causing the polypropylene cloth to shrink.

PRIOR ART
Chinese Patent CN105597391A brings out a cost-effective cleaning method of Polypropylene filter Cloth which is cleaned on line with a non-oxidizing acid with pH between 1.5 and 4 followed by cleaning followed by sterilization with alkali treatment. The acid used are one of hydrochloric acid, hydrobromic acid, hydrofluoric acid, carbonic acid, dil sulphuric acid, phosphoric acid, water soluble carboxylic organic acid (15% acid) with pH between 1.5 and 3.4. Also a mixture of 70% citric acid and 30%Sulphuric acid, 50% salicylic acid and hydrochloric acid, 10%ethanoic acid -30% ethanoic acid-60 hydrochloric acid and 40% ethanoeic acid -60%carbonic acid mixtures are recommended. A bactericide – chloro phenol derivative, OIT quarternary ammonium salt, sorbic acid and derivative of benzoate & derivative is also used. The alkaline cleaning (<1.0%) alkali wash water, sodium carbonate, potash, saleratus, Hydrogen sodium oxide molybdena, KOH, tetra ethyl disodium ethanedioic acid, Potasiumethoxide, Potassium tert-butoxide-sodium carbonate. 0.1to 1% sodium benzoate, potassium sorbate, 50% pentachloro phenol-50% OIT, 10% Chitin-90% OIT alkali lye replaced by 0.1 to 15% sodium carbonate, potash, 20%potassium hydroxide- 40%ethanedioic acid tetraacethyl disodium -40% potassium ethoxide etc. The alkaline solution 50% potassium ter butoxide-50% sodium carbonate. While the patent above talks about the wide range of chemical treatment to remove the clog in the filter, the present invention talks about the design of a system for cleaning which is much more simple. While neutralizing agent and bactericide is recommended in Chinese patent, the present invention uses only environment friendly citric acid and there is no requirement of neutralizing agent that may be required as per Chinese patent.

Patent PP-EP2316554A1 talks about cleaning of a polypropylene filter cloth that dewatered a Calcium containing slurry with water saving. The filter cloth is cleaned by spraying a tensioned filter cloth with water, steam and a mixture of both at 100 to 140 oC by spraying on the cloth at a pressure of 50 to 200 kg/cm2. The flyash slurry is dewatered. Unlike the patent, the present filter cleaning technique involves iron ore filter. While the patent talks about steam at 100 to 140 oC the present invention is done with environmentally friendly citric acid soaking followed by water jet cleaning where high efficiency cleaning is carried out.

US Patent 3397783 talks about a filter for a horizontally rotating filter cell to discharge filter cake where the filter is inverted for cleaning, with water at 300 psg pressure where crystalline growth on filter is prevented. Washing the filter fabric with a low-pressure liquid and contacting the fabric with a high-pressure liquid in an oscillating manner. The spray from the high-pressure nozzle uniformly traverses a path across the inverted surface of the horizontally moving filter cell. The high-pressure spray nozzle on produces a spiral path on the filter cleaning the surface moving radially outward to the end of the cell. The spiral movement of the spray is done outwards for 4 h and inward for 4 h with a continuously rotating horizontal rotary filter of the tilting cell type, rigidly connected to a shaft rotatably mounted. The shaft is rigidly connected to drive means for rotating and counter-rotating said shaft whereby the spray is moved in an arc-like motion and spray from said nozzle reciprocally traverses the cell from one end to the other. Time cam controls the cam uniformly rise and fall. Unlike the rotary filter in the US patent, the present invention talks about a cleaning technique suitable for cloth filters used in plate filters. The present invention talks about a soaking tank and water jet cleaning platform and usage of citric acid for cleaning as against pressurized water in the US patent.

There has been thus a need to develop a system set-up for cleaning of the clogged filter cloths used in filter press for dewatering of iron ore slurry and process to cleaning of these filter cloths to restore the cleaning efficiency and reuse in the filter press for further cleaning cycles with extended life without any deformation/distortion and damage to the filter cloths in a simple and environment friendly manner.This patent is targeted to development of a system and method for proper cleaning of the filter clothes with extended service life on reuse in filter press.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide a system and a method of cleaning clogged filter cloth used in press filter for dewatering of iron ore slurry in a simple and environment friendly manner.

A further object of the present invention is directed to a process for cleaning of clogged filter cloth of press filter using eco-friendly diluted citric acid as a cleaning agent.

A still further object of the present invention is directed to a system set-up for cleaning of clogged filter cloth of press filter that has been designed as a soaking tank resistant to the corrosion by the acid where used for contaminated filter cloths soaked to loosen the ultra-fines of iron ores.

A still further object of the present invention is directed to said system and method wherein filter cloths made of Polypropylene material is resistant to acid attack when the filter cloth is cleaned by environmentally compatible aliphatic organic acid such as citric acid and thoroughly cleaned by high pressure high volume water spray jet with filter cloth spread upon a perforated mesh type platform support.

A still further object of the present invention is directed to a process for cleaning of clogged filter cloth of press filter whereinfilter press clothes would not be allowed to dry at any stage of the handling, as it may cause the shrinkage of the polypropylene fibre knitting patterns.

A still further object of the present invention is directed to a process for cleaning of clogged filter cloth of press filter whereinlow volume of the drain liquor solution from soaking tank is collected and based on its pH value is reused along with fresh liquor,after settling iron ore residues in a container, for additional soaking of the filter cloth.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a system/assembly for clogged press filter cloth cleaning for freeing it of clogged particles and setting up for reuse and for extended life comprising

(A) a soaking chamber containing :
diluted acid liquors and valve control system to adjust the water quantity and level of dilution desired;

said soaking chamber having an anti-corrosion internal coating preferably of natural rubber and hanger means for spreading and hanging plurality of filer clothes with the diluted acid liquor content inside such that the filter clothes are always maintained wet without drying during the clog removal upon interaction of the clogged filter cloth with the acid liquor in said soaking chamber;

a drainage arrangement at the bottom operatively connected to drain out the contents from soaking chamber including the freed clogged from said filter cloth and out of the soaking chamber; and cooperative

(B) soaked filter cloth cleaning unit comprising perforated mesh type concave platform supported on stands and having a matching convex external profile for spreading the soaked filer cloth and a cooperatively disposed pressurized cleaning unit including motorized water spray system for supply of high volume flow rate in the range of 20 to 30 lpm under high pressure of 80 to 120 bar such that during pressured cleaning the soaked filter cloth is cleaned and particulates are washed through said mesh structure ; and
(C) a storage container with a water inlet on top for storage of cleaned filter cloths in water dipped condition for reuse in filter press.

A further aspect of the present invention is directed to said system for cleaning of filter cloth used in a high pressure filter press for de-watering of iron-ore slurry, which gets clogged with solid particulates, comprising

said soaking chamber/water tank with specific dimension made of a mild steel fabricated storage tank with its interior lined with natural rubber with provision for spreading and hanging of the multiple filter clothes therein with adjustable spacing;

said soaking chamber/tankcomprises a water inlet tube with valve system to fill the tank with diluted acid liquors to prescribed controlled volume for wetting and soaking of the filter cloths placed therein and a bottom drainage system which enables removal of unclogged solids from the used filters that deposit on the container bottom;

said cleaning unit having a specially configured platform set-up where the soaked clothes are spread on a concave mesh to hold the filter clothes on the structure supported by four legsto ensure dimensional stability of the filter cloths wherein height of the legs is such as to ensure that no splitting of the slurry affix with the cloth return back on the cleaned cloth for efficient and effective cleaning;

said water spray jet system connected to a high pressure hose pipe for applying water spray jet from top to bottom to clean the surfaces of the filter clothes;

said storage container for storage of cleaned filter cloths in water dipped condition,to prevent shrinkage due to drying, for reuse in filter press.

A further aspect of the present invention is directed to said system for cleaning of filter cloth wherein top of said soaking water tank has a welded stainless steel rod structure suitable for spreading and hanging of the multiple filter clothes.

A still further aspect of the present invention is directed to said system wherein a valve control system is provided to adjust the water quantity of the soaking container, ensuring maintenance of adequate level of liquor so that the filter clothes are always maintained wet without drying it.

A still further aspect of the present invention is directed to said system wherein said water jet system connected to a high pressure hose pipe is powered by an electric pump to deliver water at high pressure between 100 to 120 bar.

A still further aspect of the present invention is directed to said system wherein said water jet system comprises water spray gun having nozzles that can adjust the flow of water as well as increase or decrease the spray area of filter cloth cleaning or impact area that can be adjusted through the nozzle of spray gun, whereby the water jet spray device is controlled to adjust the volume and pressure such that the damage to the filter cloth or distortion to the cloth is avoided.

A still further aspect of the present invention is directed to a process for cleaning clogged press filter cloth cleaning for freeing it of clogged particles and setting up for reuse and for extended life involving the system /assembly as described above comprising:

(a) Soaking of clogged filter cloth in dilute acid solution in said soaking chamber following :
(i) hanging the used clogged filter clothes inside soaking chamber;
(ii) filling the soaking chamber with a 25 to 50% diluted acid liquor to wash the filter clothes and to top the fresh diluted liquor to maintain the level of soaking chamber such that the used filter cloth stayed submerged throughout the soaking duration;
(iii) withdrawing the separated residues from filter cloth accumulated during soaking throughdrainage pipe connected at the bottom of the soaking chamber,
(iv) controlling the outflow of the acid through a valve attachment to said drainage pipe to discharge the liquid or contaminated acidic liquor for settling and optionally for reutilization based on the pH value;
(b) subjecting soaked filter cloth to cleaning in a soaked filter cloth cleaning unit involving spray water jet comprising:
(i) taking out the soaked filter cloth after completion of the soaking period, and spreading upon said perforated mesh type platform for pressurized spray cleaning of filter cloth without obstruction below the perforated base to hold water or contamination due to soiled liquid;
(ii) applying high pressure jet from water spray system for desired cleaning of clogged particles from filter cloths including woven synthetic polymeric materials such as polypropylene and its derivatives;
(c) storing the cleaned filter cloths in a storage container dipped inside water in a container of appropriate size to accommodate the size of filter cloth of given number in a batch avoiding dimensional variation making it fit for reuse in filter press.

A still further aspect of the present invention is directed to said process for cleaning of clogged filter cloth comprising the steps of

(a) Soaking of clogged filter cloth in dilute acid solution in soaking tank comprising:
(i) hanging the used clogged filter clothes inside soaking tank from welded stainless steel structure provided at top of soaking tankensuring proper spacing between the longitudinal rods;
(ii)filling the soaking tank with a 25 to 50% diluted citric acid to wash the filter clothes and to top the fresh diluted liquor to maintain the level of soaking tank so that the used filter cloth stayed submerged throughout the soaking duration;
(iii) withdrawing the separated residues from filter cloth accumulated during soaking throughone drainage pipe connected at the bottom of the tank,
(iv) controlling the flow of the acid through a valve attachment to said drainage pipe to discharge the liquid or contaminated acidic liquor for settling and reutilization based on the pH value;
(b) subjecting soaked filter cloth to spray water jet comprising:
(i)taking out filter cloth after completion of the soaking period, and spreading upon a perforated mesh type platform for pressurized spray cleaning of filter cloth without obstruction below the perforated base to hold water or contamination due to soiled liquid;
(ii)applying high pressure jet from water spray system for desired cleaning of clogged particles from filter cloths made of woven synthetic polymeric materials such as polypropylene and its derivatives;
(c) storing the cleaned filter cloths dipped inside water in a container of appropriate size to accommodate the size of filter cloth of given number in a batch avoiding dimensional variation making it fit for reuse in filter press.

A still further aspect of the present invention is directed to said process wherein said soaking is carried out in a tank chamber that can accommodate filter cloth of 3750 mm length and 2050 mm width size and total 6 filter cloths per batch that are processed for soaking duration of 10 to 12 hours.

Another aspect of the present invention is directed to said process wherein citric acid with its dilution ranging between 25 and 50% used for soaking the filter clothes at ambient temperature with soaking duration of 10-12 hours for a batch whereby the clogged particulates in the filter cloth are loosened and separated residue is deposited at the bottom of the soaking tank that is drained out.

Yet another aspect of the present invention is directed to said process wherein said spraying water jet comprising water spray introduced with a solid stream type nozzle which can be operated at 20 to 30 lpm with 80 to 120 bar pressure to cleaning and rinsing of the filter cloth whereby a cloth can be cleaned in less than 30 min time.

A still further aspect of the present invention is directed to said process wherein the process of cleaning filter cloth is implemented in a safe and environment friendly manner free of contamination of cleaned filter cloth and recycling of used acid solution.

A still further aspect of the present invention is directed to said process enable cleaning of filter cloth that possess 95% efficiency and capable to be reutilized for 1500 to 2000 more dewatering cycles in filter press.

The above and other aspects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Preferred embodiments of the invention are described below, with reference to the drawings, wherein like numerals are used to refer to the same or similar elements:
Figure 1: is a simplified schematic diagram of first process unit of filter cloth soaking used for loosening the iron ore ultra-fines and sticky materials with the filter cloth. Used filter cloth after press filter application, directly submerged in this system.

Figure 2: is a simplified schematic side view of high volume (20-30 Lpm), high pressure (80-120 bar) water spraying system.

Figure 3: is the schematic of filter cloth cleaning platform where filter cloth laid upon this and water jet applied to clean the residues of iron ore fines.

Figure 4: is the view of set up for storage of cleaned filter cloth attached with water supply system.

Figure 5: Block diagram to illustrate the complete process where all the subsystems like soaking tank, spreading of soaked cloth platform, applying water spray jet and storing in water tank in dipped condition.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS
The present invention provides a method of cleaning filter cloth of press filter using eco-friendly diluted citric acid as a cleaning agent. The device that has been designed is resistant to the corrosion by the acid where used or contaminated filter cloths soaked to loosen the ultra-fines of iron ores.

The present filter clothes in operation, is made of Polypropylene material and is resistant to acid attack when the filter cloth is cleaned by environmentally compatible aliphatic organic acid such as citric acid. The polypropylene fibre has a high tolerance for both acidic and alkali cleaning solution.

The iron ore fines clogged in the filter cloth, is loosened in a soaking tank, where the filter cloth is spread on an adjustable hanging system. The tank has an arrangement to remove the residues settled at the bottom of the tank through a drain arrangement. The drainage of used acid liquor may be further re-utilized after settling iron ore residues in a container. The low volume of the drain liquor solution is collected and based on its pH value is reused along with fresh liquor for additional soaking of the filter. The soaking of the filter cloth in acid liquor loosens the sticky iron ore fines. The filter clothes are placed in a perforated platform designed and fabricated to ensure high volume water (20 to 30 lpm) at high pressure water (80 to 120 bar) spray system. Generally, hard brushing is not practiced as abrasions may damage or deteriorate the performance of the filter cloth resulting in shortening the life of the filter cloth. It was also ensured that the filter press clothes were not allowed to dry at any stage of the handling, as it may cause the shrinkage of the polypropylene fibre knitting patterns.

The soaking tank inner walls coated with acid resistant material that is natural rubber in form of 2 mm sheets. The collected residue of iron ore ultra-fines during soaking may be recirculated to the system as a raw material for pellet making. Water is used to clean the filter cloth through high pressure jets is not hazardous during filter cloth washing as high volume (20 – 30 Lpm) of water nullify the acidic nature. High pressure (80-120 bar) and high volume water(20-30 Lpm) jet spray system remove all the sticky ultra-fines those involve in blocking the polypropylene knitting space and fibres. As a result, the porosity has been regained in this process. The present invention has been made to solve the above-mentioned problems, and aims to provide a device and method for cleaning a filter cloth of a filter press that are capable of restoring a filter cloth by effectively cleaning the filter cloth while reutilization of acid liquor where ever it has been involve during cleaning of filter cloths and not required any waste water treatment system.

A simplified schematic view of soaking tank is given as in Figure 1. The tank is designed to soak the filter cloth which has enhances the cleaning efficiency. A 5mm thick mild steel sheet is used for the fabrication of the tank 1.1. The inner walls of the tank werecoated with natural rubber 1.2. An arrangement to hang the used clogged filter clothes that consisted of welded stainless steel structure made of 10 mm thick rods 1.2. A cross welded rod 1.3 ensures proper spacing between the longitudinal rods. The structural arrangement enables hanging of filter clothes on the welded rod structure. The tank is filled with a 25 to 50% dilutedcitric acid to wash the filter clothes. At the bottom of the tank, one drainage pipe 1.5 is connected to withdraw the separated residues from filter cloth accumulated during soaking. This drainage pipe system has an attachment of valve 1.6 to control the flow of the acid to discharge the liquid or contaminated acidic liquor for settling and reutilization based on the pH value. An arrangement 1.7 has been provided to top the fresh diluted liquor to maintain the level of soaking tank so that the used filter cloth stayed submerged throughout the soaking duration.

After completion of the soaking period, the filter cloth was taken out and spread upon a perforated mesh type platform, where pressurized spray cleaningas shown in figure 2. Theplatform profile is concave, having mesh 2.1 and 2.2, along the width and length respectively. The whole perforated mesh supported by a frame having a specific length 4000 mmand width 2400 mm. During spray cleaning, it was ensured that there is no obstruction below the perforated base to hold water or contamination due to soiled liquid. To avoid such contamination,legs of the frame having 1500 mm heighthas been providedto support the whole structure.

The soaked filter cloth was then placed on the top of the perforated mesh as in Figure 2. The schematic of the complete cleaning device for the filter cloth is shown in Figure 3. High volume flow rate (20 to 30lpm)and high pressure (80 to 120 bar) water spray system is built with a high power motor 3.1 (2000 Watts) to transfer the water cleaning medium. The high volume flow rate and high pressure water is transferred by the motor 3.1 through a high pressure(150bar) hose 3.2 to the water spray gun 3.3. The spray gun has an adjustable spray nozzle 3.4. This spray nozzle is having arrangement to minimize or maximize the water spray area on the filter cloth.

The filter clothes are made of woven synthetic polymeric materials such as polypropylene and its derivatives. The filter clothes are manufactured in weaving textile looms using individual strands of synthetic yarn. The threads are spun together to produce filter clothes designed porosity level for specific dewatering applications.The filter clothes, made up of polypropylene material may change its shape or show dimensional irregularities in service when the clothes are dried. To avoid dimensional variations, the filter clothes are kept in wet condition without drying the clothes. Usually polymer like polypropylene chains become more mobile and are more likely to move and rearrange themselves as once treated with water and dried. Such few cycles may further distort the polymer chain structure and cause dimensional variation.To maintain the dampness, An arrangement to store the cleaned filter clothes stabilized and referred in Figure 4. An open,4 mm thick mild steel container 4.1 was fabricated with its length and width accommodating the size of the filter cloth. The depth of the container,depends on the storage quantity of the filter clothes. Filter cloth 4.2 having fixing hole 4.3 layered inside the water filled container. The container has a facility for top upof water provided by a tap 4.4, which is attached to a valve 4.5 to switch on or switch off the water supply, considering the numbers of clothes that shall be maintained in wet condition.

Accompanying Figure 5 shows the Block diagram to illustrate the complete process where all the subsystems like soaking tank, spreading of soaked cloth platform, applying water spray jet and storing in water tank in dipped condition. Inter-connection of different stages of the process as reflected in Figure 5 indicate that the whole setup and process parameters to clean the filter cloth of press filter are dependent with each other and process can be efficiently operated only when every single parameters are well within the prescribed conditions. The set up parameters will not provide efficient cleaning of clogged filter cloth if the concentration level will not matched with prescribed level. The process may show less efficiency if the soaking tank residues of clogged particles settled at bottom not removed on regular interval through valve system may not effective for loosening of clogged particles of filter cloth. High volume and high pressure water spray system may be not efficient to remove the clogged particles. Similarly if the cloth platform set up will be not having stuffiest height, the high pressure water jet may cause spilled over clogged material again on the top or bottom portion of the cloth. Further even after efficient cleaning of filter cloth, if the filter cloth not stored in the water filled tank, the polymer threads of filter cloth may get disturb due to non-uniform temperature or other environmental variations. Such conditions may also cause the distortion in weaving pattern of the filter cloth. Overall the whole set up is relates with every stage of the process and cumulative performance of the system can only provide the efficient cleaning of clogged filter cloth for re utilization in press filter system.

As described in Table 1, there are total 12 press filter units installed in pellet making plant to supply uninterrupted supply of iron fines. Each press filter accommodates 120 cloth filters at a given instant. Polypropylene synthetics utilized for cloth filters. Pilot scale trials taken in a chamber fabricated as 2500 mm length, 2100 mm width and 5000 mm depth. This chamber can accommodate filter cloth of 3750 mm length and 2050 mm width size and total 6 filter cloths per batch can be processed for soaking duration of 10 to 12 hours. Acid concentration maintained by 25 to 50% level and checked in every 12 hours cycle through pH value. Citric acid used as an economical, efficient and user-friendly liquor. A water spray system introduced with a solid stream type nozzle which can be operated at 20 to 30 lpm with 80 to 120 bar pressure to cleaning and rinsing of the filter cloth. With these process parameters of water spray system a cloth can be cleaned in less than 30 min time. Equation 1 has been applied to design the spray nozzle size based on required water flow rate and pressure,
Qn = 28.9XD2X v P (Eq-1)
Where,
Qn is the water flow rate from the nozzle (lpm)
D is the nozzle diameter (mm)
And P is the pressure at nozzle (bar)

After 3400 to 3500 numbers of press filter cycles, the filter cloth lost 75-80 % of its capacity and dewatering become very difficult.There may be multiple reasons for the decreased efficiency of filter cloth in press filter used for dewatering. Some of the reasons include, clogging where the filter cloth can become clogged with solids, particulates, or other materials being filtered. This clogging reduces the open area of the cloth and restricts the flow of liquid through the cloth, leading to decreased dewatering efficiency over time Another reason is blinding , where the filter cloth may experience blinding, which occurs when fine particles become trapped in the openings of the cloth, reducing its permeability and preventing efficient dewatering. Sometimes chemical fouling, wear and tear, or may be poor maintenance also decrease the dewatering efficiency of the filter cloth over time.Cleaned filter cloth possess 95% efficiency and can be reutilized for 1500 to 2000 more dewatering cycles. This cleaned filter cloth may be utilized multiple times after rewashing, depends upon the cloth quality and damages.Citric acid is effective at removing mineral deposits and scaling from various surfaces. Once acid liquor used for several batch applications and pH lower down, initially acid top up done to balance the pH and reactivity of acid. After multiple cycles of water clothing treatment, the liquor collected in a tank, allowed to settle down all the iron fines andother substances. The settled material tapped out from the system and recheck the pH of the clean acid liquor. This liquor further top up with fresh liquor and this cycle continues. There is no acid liquor discharged from the system and utilized in recirculation system.

Table 1. The final condition for cleaning of the clogged filter cloth
S No Parameters Details
1. Type of filter press Plate type
Numbers of filter 12
2. No. of clothes in a batch 120
3. Filter cloth material Polypropylene cloth
4. Filter Soaking Tank
Length= 2500 mm
Width = 2100 mm
Height= 5000mm
5. No. of filter clothes loaded to the tank for washing (1 Batch) 6
6. Dimension of each filter cloth ( Length x width) in mm 3750x2050
7. Acid concentration initially added in soaking tank 25 to 50 %
8. Acid used Citric acid
9. Volume of acid used 4000 lit
10. Reuse of citric acid Yes ( in circulation)
11. No of clothes added in the soaking stage 100
12. Duration of soaking 10 to 12 hours
13. Water jet cleaning on the platform yes
14. Pressure of water jet 80 to 120 bar
15 Volume flow rate of water 20 to 30 lpm
16. Total quantity of water used 12000 lt.
17. Spray nozzle design Solid stream type
18.. Time taken to clean a single cloth 25-30 min
19 Life of each filter clothes >60% enhanced
20 No. of times a cloth is reused 1 to 2
21 Filtration efficiency in the new/cleaned cloth 95%
22 Filtration efficiency when the filter is discarded 20-25%

The Table 1 above illustrate that Filter cloth cleaning efficiency vary with varying parameters of this innovative process set up. The efficiency varies from 40% to 70 % when the system operated with different process parameters. Soaking of filter cloth in soaking tank is the 10-12 Hours directly related with concentration of diluted liquor. High concentration of liquor may increase the efficiency of loosening the slurry stick with filter cloth. High concentration of liquor (>50%) may also create acidic fumes or techno economically not feasible. Diluted liquor (25% to 50 %) is very suitable for this innovative process set up. One more demerits to operate with High concentration of liquor is it may further damage the filter cloth and during re-utilization, not in the condition to sustain the high pressure of press filter cloth operations. It is also considered that the high volume (20-30 LPM) and high pressure (80-120 bar) water spray system with soil stream type nozzle is having capacity so that a little weak portion of the filter cloth may be torn during high pressure water spray, if the concentration of liquor is not optimized. The dimensions of the soaking tank and platform (to hold the cloth) for water spray is designed so that the used filter cloth can be accommodated within so that no folding or overlapping takes place and allowed maximum surface area of the cloth exposed for the different process sections.

The Inventive merit of present invention reside in the process comprising of a setup of different sub-systems and processes cumulatively work to increase the efficiency of filter cloth while removing the clogged particles from the cloth. This innovative process utilizing diluted citric acid with explained process parameters can only provide the desired cleaning efficiency of the filter cloth. The concentration of citric acid, soaking parameters (duration and conditions of cloth soaking), spreading soaked cloth on the platform (stand height, no wrinkles or creases on the cloth), high volume and high pressure water spray on the cloth while avoiding the clogged particles further spilling on the cloth, followed by storing the cleaned filter cloth in a water filled storage tank to avoid shrinkage of cloths. The setup allows efficiently cleaning the filter cloth and avoiding any physical damage so that filter cloths can be utilized further in press filter system.

It is thus possible by way of the present invention to develop a system set-up and a process for the batch wise cleaning of clogged solid particulates in a filter cloth used in a high pressure filter press wherein the clogged filter cloths aresoaked in dilute citric acid solution in asoaking tank to loosen the clogged particles on cloth, spreading the soaked cloths on a perforated mesh type concave platform structure and subjecting to high pressure and high volume water spray jet for cleaning of particles and finally storing the cleaned filter cloths in water storage tank in water dipped condition to ensure reuse in filter press with higher efficiency and longer service life. The process set-up ensures achieving a cleaning efficiencyas high as 95% of filter cloths after cleaning. The method of cleaning ensures that the choked filter clothes restoreextended life for 2000-2400 cycles to reuse in press filter dewatering system.The cleaning of filter clothes in the entire process is carried out in an environment friendly manner at ambient temperature and does not pose health hazard ensuring safety of personnel.

, Claims:We Claim:
1. A system/assembly for clogged press filter cloth cleaning for freeing it of clogged particles and setting up for reuse and for extended life comprising

(A) a soaking chamber containing :
diluted acid liquors and valve control system to adjust the water quantity and level of dilution desired;

said soaking chamber having an anti-corrosion internal coating preferably of natural rubber and hanger means for spreading and hanging plurality of filer clothes with the diluted acid liquor content inside such that the filter clothes are always maintained wet without drying during the clog removal upon interaction of the clogged filter cloth with the acid liquor in said soaking chamber;

a drainage arrangement at the bottom operatively connected to drain out the contents from soaking chamber including the freed clogged from said filter cloth and out of the soaking chamber; and cooperative

(B) soaked filter cloth cleaning unit comprising perforated mesh type concave platform supported on stands and having a matching convex external profile for spreading the soaked filer cloth and a cooperatively disposed pressurized cleaning unit including motorized water spray system for supply of high volume flow rate in the range of 20 to 30 lpm under high pressure of 80 to 120 bar such that during pressured cleaning the soaked filter cloth is cleaned and particulates are washed through said mesh structure ; and
(C) a storage container with a water inlet on top for storage of cleaned filter cloths in water dipped condition for reuse in filter press.

2. The system as claimed in claim 1 for cleaning of filter cloth used in a high pressure filter press for de-watering of iron-ore slurry, which gets clogged with solid particulates, comprising

saidsoaking chamber/water tank with specific dimension made of a mild steel fabricated storage tank with its interior lined with natural rubber with provision for spreading and hanging of the multiple filter clothes therein with adjustable spacing;

said soaking chamber/tankcomprises a water inlet tube with valve system to fill the tank with diluted acid liquors to prescribed controlled volume for wetting and soaking of the filter cloths placed therein and a bottom drainage system which enables removal of unclogged solids from the used filters that deposit on the container bottom;

said cleaning unit having a specially configured platform set-up where the soaked clothes are spread on a concave mesh to hold the filter clothes on the structure supported by four legsto ensure dimensional stability of the filter cloths wherein height of the legs is such as to ensure that no splitting of the slurry affix with the cloth return back on the cleaned cloth for efficient and effective cleaning;

said water spray jet system connected to a high pressure hose pipe for applying water spray jet from top to bottom to clean the surfaces of the filter clothes;

said storage container for storage of cleaned filter cloths in water dipped condition,to prevent shrinkage due to drying, for reuse in filter press.

3. The system for cleaning of filter cloth as claimed in claim 1 or 2 whereintop of said soaking water tank has a welded stainless steel rod structure suitable for spreading and hanging of the multiple filter clothes.

4. The system as claimed in anyone of claims 1 to 3 wherein a valve control system is provided to adjust the water quantity of the soaking container, ensuring maintenance of adequate level of liquor so that the filter clothes are always maintained wet without drying it.

5. The system as claimed in anyone of claims 1 to 4 wherein said water jet system connected to a high pressure hose pipe is powered by an electric pump to deliver water at high pressure between 100 to 120 bar.

6. The system as claimed in anyone of claims 1 to 5 wherein said water jet system comprises water spray gun having nozzles that can adjust the flow of water as well as increase or decrease the spray area of filter cloth cleaning or impact area that can be adjusted through the nozzle of spray gun, whereby the water jet spray device is controlled to adjust the volume and pressure such that the damage to the filter cloth or distortion to the cloth is avoided.

7. A process for cleaning clogged press filter cloth cleaning for freeing it of clogged particles and setting up for reuse and for extended life involving the system /assembly as claimed in anyone of claims 1 to 6 comprising :

(a) Soaking of clogged filter cloth in dilute acid solution in said soaking chamber following :
(i) hanging the used clogged filter clothes inside soaking chamber ;
(ii) filling the soaking chamber with a 25 to 50% diluted acid liquor to wash the filter clothes and to top the fresh diluted liquor to maintain the level of soaking chamber such that the used filter cloth stayed submerged throughout the soaking duration;
(iii) withdrawing the separated residues from filter cloth accumulated during soaking throughdrainage pipe connected at the bottom of the soaking chamber,
(iv) controlling the outflow of the acid through a valve attachment to said drainage pipe to discharge the liquid or contaminated acidic liquor for settling and optionally for reutilization based on the pH value;
(b) subjecting soaked filter cloth to cleaning in a soaked filter cloth cleaning unit involving spray water jet comprising:
(i) taking out the soaked filter cloth after completion of the soaking period, and spreading upon said perforated mesh type platform for pressurized spray cleaning of filter cloth without obstruction below the perforated base to hold water or contamination due to soiled liquid;
(ii) applying high pressure jet from water spray system for desired cleaning of clogged particles from filter cloths including woven synthetic polymeric materials such as polypropylene and its derivatives;
(c) storing the cleaned filter cloths in a storage container dipped inside water in a container of appropriate size to accommodate the size of filter cloth of given number in a batch avoiding dimensional variation making it fit for reuse in filter press.

8. The process for cleaning of clogged filter cloth as claimed in claim7 comprising the steps of

(a) Soaking of clogged filter cloth in dilute acid solution in soaking tank comprising:
(i)hanging the used clogged filter clothes inside soaking tank from welded stainless steel structure provided at top of soaking tankensuring proper spacing between the longitudinal rods;
(ii)filling the soaking tank with a 25 to 50% diluted citric acid to wash the filter clothes and to top the fresh diluted liquor to maintain the level of soaking tank so that the used filter cloth stayed submerged throughout the soaking duration;
(iii)withdrawing the separated residues from filter cloth accumulated during soaking throughone drainage pipe connected at the bottom of the tank,
(iv)controlling the flow of the acid through a valve attachment to said drainage pipe to discharge the liquid or contaminated acidic liquor for settling and reutilization based on the pH value;

(b)subjecting soaked filter cloth to spray water jet comprising:
(i) taking out filter cloth after completion of the soaking period, and spreading upon a perforated mesh type platform for pressurized spray cleaning of filter cloth without obstruction below the perforated base to hold water or contamination due to soiled liquid;
(ii) applying high pressure jet from water spray system for desired cleaning of clogged particles from filter cloths made of woven synthetic polymeric materials such as polypropylene and its derivatives;
(c)storing the cleaned filter cloths dipped inside water in a container of appropriate size to accommodate the size of filter cloth of given number in a batch avoiding dimensional variation making it fit for reuse in filter press.

9. The process as claimed in anyone of claims 7 or 8 wherein said soaking is carried out in a tank chamber that can accommodate filter cloth of 3750 mm length and 2050 mm width size and total 6 filter cloths per batch that are processed for soaking duration of 10 to 12 hours.

10. The process as claimed in anyone of claims 7 to 9 wherein citric acid with its dilution ranging between 25 and 50% used for soaking the filter clothes at ambient temperature with soaking duration of 10-12 hours for a batch whereby the clogged particulates in the filter cloth are loosened and separated residue is deposited at the bottom of the soaking tank that is drained out.

11. The process as claimed in anyone of claims 7 to 10 wherein said spraying water jet comprising water spray introduced with a solid stream type nozzle which can be operated at 20 to 30 lpm with 80 to 120 bar pressure to cleaning and rinsing of the filter cloth whereby a cloth can be cleaned in less than 30 min time.

12. The process as claimed in anyone of claims 7 to 11 wherein the process of cleaning filter cloth is implemented in a safe and environment friendly manner free of contamination of cleaned filter cloth and recycling of used acid solution.

13. The process as claimed in anyone of claims 7 to 12 enable cleaning of filter cloth that possess 95% efficiency and capable to be reutilized for 1500 to 2000 more dewatering cycles in filter press.

Dated this the 20th day of November, 2023
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199