How to choose the right box-type filter?

When choosing a suitable box-type filter, it is necessary to comprehensively consider the characteristics of the medium, processing requirements, equipment performance, and cost. The following is a systematic selection process and key point analysis:
I. Clarify the basic parameters of the medium
1. Medium type and state
Reference for selecting core concerns in medium classification
For liquid media with high viscosity, turbidity, corrosiveness, and particle size of suspended solids (such as syrup), large-pore filter materials are required. For corrosive media (such as strong acids), polypropylene (PP) and polytetrafluoroethylene (PTFE) filter materials should be selected.
For gas media with dust content, temperature, dew point, and chemically active high-temperature gases (≥120℃), high-temperature resistant filter materials (such as glass fiber) are required. Oily gases need to be combined with oil-removing filter elements.
The characteristics of the filter cake for solid-liquid mixed media (viscosity, particle size distribution) and solid content: If the solid content is high (>10%), plate and frame filters (with a large filter cake holding space) are preferred. Viscous filter cakes require anti-clogging filter cloths (such as monofilament filter cloths).
2. Quantification of key parameters
Temperature: The temperature resistance of the filter material should be at least 20℃ higher than the medium temperature (for example, PP filter material ≤90℃, PTFE filter material ≤260℃).
Pressure: The working pressure should match the design pressure of the filter (for example, if 0.1-0.6MPa, a normal pressure type should be selected; for high-pressure working conditions, a pressure-resistant housing should be custom-made).
Corrosiveness: Select the filter material and shell material based on the pH value and chemical composition of the medium (such as chloride ion concentration) (refer to the table below)

Medium characteristics, recommended materials, and contraindicated materials
Strong acids (pH<2), PTFE, titanium alloy, stainless steel (such as 304 are prone to corrosion by hydrochloric acid.
Strong alkali (pH>12) fluororubber sealing parts, PP aluminum alloy, copper materials
Organic solvents (such as acetone), nylon filter materials, PVDF shells, and common rubber seals (prone to swelling)
Second, determine the processing capacity and precision requirements
1. Processing flow rate and filtration area
Flow calculation: Select the filtration area of the filter based on the processing capacity per unit time (m³/h), usually following the empirical formula:
Filtration area (㎡) = flow rate (m³/h) ÷ Filtration rate (m³/㎡·h)
The water filtration rate is approximately 1-5 m³/㎡ · h, and the paint filtration rate is approximately 0.5-1 m³/㎡ · h.
Reference equipment specifications
Small-sized: Cylindrical filters with a processing capacity of less than 10 m³/h and an optional number of 1 to 4 filter cartridges.
Medium: 10-50 m³/h, available in plate and frame type (with 10-20 filter plates) or multi-cylinder type (6-12 filter cartridges).
Large: >50 m³/h, multi-unit parallel plate and frame or candle filters need to be customized.
2. Filtration accuracy requirements
Particle size control: Select the precision of filter materials based on the particle size of impurities in the medium (e.g.
Clarification filtration: 5-20μm (such as drinking water);
Precision filtration: 0.1-5μm (such as for liquid medicine);
Sterilizing filtration: 0.22μm (sterilizing grade filter element required).
Accuracy verification: Confirm the interception effect of the filter material through pre-filtration tests (such as using a particle counter to detect the impurity content after filtration).
Iii. Select the type and structure of the filter
1. Select the type based on the structural type
Type: Plate and frame filter, cartridge filter, bag filter
Structural features: Multiple filter plates are stacked, with filter cloths sandwiched between the plates and frames. Filter elements are inserted into filter cartridges, and single or multiple combined filter bags are placed inside filter baskets, with flange sealing
The applicable scenarios include high solid content (1-30%), high precision requirements for filter cake recovery (0.1-100μm), medium to large flow coarse filtration (10-500μm), and convenient filter bag replacement
The advantages include large filter cake capacity, adjustable filtration area, stable precision, high degree of automation, low cost, and high efficiency in replacing filter bags
Typical cases include chemical sludge dewatering, filtration of traditional Chinese medicine extracts, lubricating oil filtration, preparation of electronic ultrapure water, pretreatment of sewage treatment, and ink filtration
2. Select the model based on the degree of automation
Manual type: Suitable for small-batch and intermittent production (such as laboratory filtration), the filter material needs to be replaced manually.
Semi-automatic type: Equipped with an automatic backwashing system (such as timed backwashing of cylindrical filters), reducing manual intervention.
Fully automatic type: Integrates functions such as pressure sensing, filter material life monitoring, and automatic bag changing (such as in industrial continuous production scenarios).
Four. Consider the material and sealing design
The shell material matches that of the filter material
Shell material
Stainless steel (304/316L): General-purpose, resistant to weak acids and weak alkalis;
Polypropylene (PP): Acid and alkali resistant, suitable temperature ≤90℃;
Carbon steel lined with rubber: Moderate corrosion resistance, low cost.
Filter material selection table

Filter material type, material precision range, temperature resistance/corrosion resistance
Woven filter cloth made of polyester (PET), 5-100μm, resistant to acid but not to strong alkali, with a temperature resistance of ≤130℃
Non-woven fabric polypropylene (PP) 1-50μm, acid and alkali resistant, temperature resistance ≤90℃
The pleated filter cartridge, polyethersulfone (PES) 0.1-10μm, has a temperature resistance of ≤80℃ and is suitable for the filtration of liquid medicine and water
Sintered filter element stainless steel powder 0.5-100μm, high-temperature resistant (≤400℃), corrosion-resistant (surface treatment required)
2. Key points of sealing design
Sealing form
Flange sealing: Suitable for high-pressure scenarios (≥0.6MPa), and requires a metal wound gasket.
O-ring sealing: Commonly used are nitrile rubber (oil-resistant) and fluorine rubber (acid, alkali, and high-temperature resistant).
Leak-proof test: When selecting the model, require the supplier to provide a sealing performance report (such as a leakage rate of ≤0.1% under pressure test).
V. Cost and Maintenance Efficiency Assessment
Full life cycle cost calculation
Initial investment: Plate and frame type (medium) < bag type (low) < cylinder type (high, high cost of precision filter elements).
Operating cost
Filter material replacement frequency: Bag-type filter bags (replace weekly) > pleated filter elements (3-6 months) > sintered filter elements (1-2 years);
Energy consumption: The energy consumption of the fully automatic backwashing type filter (requiring a pump and control system) is higher than that of the manual type.
Maintenance cost: The plate and frame type requires regular cleaning of the filter plates, resulting in relatively high labor costs. The cylindrical filter has a high degree of automation and low maintenance costs.
2. Considerations for maintaining convenience
Filter material replacement efficiency: It only takes 5 to 10 minutes to replace the filter bags of the bag filter, which is suitable for scenarios with frequent replacement.
Cleaning method: Backwashable filter elements (such as sintered filter elements) are more convenient to maintain than non-backwashable types (such as pleated filter elements).
Vi. Customized Requirements for Special Scenarios
1. Explosion-proof/clean environment
Flammable and explosive environment: Select explosion-proof motors (such as Ex d IIB T4) and anti-static filter materials (such as carbon fiber-coated filter cloth);
Cleanroom (such as pharmaceutical): It must comply with GMP standards, and mirror-polished stainless steel shells (roughness Ra≤0.8μm) and sterilizing grade filter elements should be selected.
2. High-temperature/high-pressure working conditions
High-temperature gas filtration: Select metal sintered filter elements + insulated shells (such as 316L stainless steel + rock wool insulation layer);
High-pressure liquid filtration (>1MPa): Customized pressure-resistant housing (design pressure ≥1.5 times the working pressure), equipped with rupture disc safety device.
Vii. Summary of the Selection Process
Parameter collection: Medium characteristics (temperature, pressure, corrosiveness), processing capacity (m³/h), accuracy (μm);
Preliminary type selection: Choose plate and frame type, cylinder type, or bag type based on solid content and precision.
Material matching: Select the material of the shell and filter material based on corrosiveness, and leave a margin for temperature resistance.
Specification calculation: Determine the filtration area based on the flow rate and select the number of filter plates or filter cartridges.
Cost assessment: Compare the initial investment with the filter material replacement cycle to balance the cost performance.
Customization confirmation: For special scenarios (explosion-proof, high-temperature), technical solutions need to be communicated with the supplier.
Reference for selection cases
Scene: A certain chemical plant needs to filter wastewater containing hydrochloric acid (pH=1), with a flow rate of 20m³/h, impurity particle size ≥5μm, and normal temperature and pressure.
Selection steps
The medium is highly corrosive. The shell is made of PP material, and the filter material is PP non-woven fabric (acid and alkali resistant, with a precision of 5μm).
The processing capacity is 20m³/h. Calculated at a filtration rate of 2m³/㎡ · h, the required filtration area is 10㎡. A plate and frame filter (15 filter plates, each with an area of 0.7㎡) is selected.
Fluororubber O-rings are selected as the sealing parts to prevent hydrochloric acid leakage.
Configure an automatic backwashing system to reduce the frequency of manual cleaning of the filter cake.
Through systematic selection based on the above dimensions, it can be ensured that the box-type filter not only meets the process requirements but also takes into account economy and reliability. It is recommended to cooperate with the supplier to conduct medium filtration tests to verify the interception effect of the filter material and the stability of equipment operation.