Basic Concept of Fluidized Bed

When a fluid moves upward through a bed of particles at varying speeds, several situations may occur.

Fixed Bed – When the fluid velocity is low, the fluid flows through the gaps between stationary particles, and this type of bed is known as a fixed bed.

An initial or critical fluidized bed – as the fluid velocity increases to a certain extent, the particles begin to loosen and their positions adjust within a certain range, the bed layer slightly expands, but the particles are still unable to move freely. At this point, the bed layer is in an initial or critical fluidization state.

A fluidized bed—when the fluid velocity increases to the point where all particles are suspended and randomly move within the upward flowing gas or liquid, the frictional force between the particles and the fluid is balanced with their net gravitational force. Subsequently, the bed height 'l' will increase with the rise in fluid velocity. Such a bed is referred to as a fluidized bed.

A dilute phase conveying bed – once the flow rate increases to a certain critical value, the interface on the fluidized bed vanishes, and the particles disperse into suspension within the air flow, being carried away by it. This type of bed is known as a dilute phase conveying bed.

2. Characteristics of Fluidized Bed

The gas-solid movement in a fluidized bed resembles that of boiling liquid and exhibits properties similar to those of a liquid in many aspects. A fluidized bed possesses the flow characteristics of a liquid, allowing granular material to be ejected from small holes in the container walls, flowing from one container to another like a liquid. Additionally, objects lighter than the bed density can be easily pushed into the bed and, upon release, they bounce back and float on the surface of the bed.

When the container tilts, the upper surface of the bed remains level, and when two beds are connected, their bed surfaces automatically adjust to the same level; the pressure change between any two cross-sections within the bed is roughly equal to the weight of the bed per unit area between those sections.

3. Granulated Fluidized Bed Sewage Treatment Technology

The granular fluidized bed is a novel water treatment technology proposed by combining the principles of quasi-steady-state operation in chemical engineering and reaction engineering theory with the practical experience of sludge engineering. The main technical indicators of this technology are as follows:

The initial chemical coagulation reaction is completed in a hydraulic mixer, with a hydraulic retention time of less than 1 minute; the granulation reaction is completed within an upward flow mechanical stirrer, with a mechanical stirrer intensity (g-value) of approximately 30-60 seconds, and a hydraulic retention time of 10-20 minutes.

The solid-liquid separation is achieved in the solid-liquid separation zone at the top of the self-granulating fluidized bed, with a hydraulic retention time of 5-10 minutes.

Sludge is automatically concentrated during separation. For systems primarily composed of inorganic suspended particles, the separation sludge moisture content can reach 80%-85%. In systems where organic components coexist with inorganic suspended matter, the separation sludge moisture content is 90-95%.

The separated water typically has an SS concentration less than 5mg/L, while the separated water SS concentration usually falls below 1mg/L after the separation zone is equipped with an enhanced separation auxiliary device.

Application Scope: Raw Water (Wastewater, Effluent) SS concentration of 1000-20,000 mg/L, COD not exceeding 1000 mg/L.

This technology is achieved through a specially designed integrated unit. Its main features include short hydraulic retention time, compact size, minimal land requirement, wide applicability, flexible use, high processing efficiency, and the ability to simultaneously complete solid-liquid separation and sludge concentration.

This technology is widely applicable to high-turbidity raw water treatment, high suspended solid concentration wastewater treatment and reuse, sludge thickening in waterworks and urban wastewater treatment plants, construction site wastewater treatment, disaster relief water treatment, and more.

4. Current Application Status

The granular fluidized bed technology, capable of efficiently separating returned liquids, is widely used in high-turbidity water supply treatment, high suspended solids concentration wastewater treatment and reuse, sludge concentration in water plants and urban sewage treatment plants, construction site wastewater treatment, and disaster relief water treatment.

Utilizing the granule-type high-efficiency liquid separation technology for treating high suspended solids concentration industrial wastewater offers advantages over traditional treatment processes in the following aspects:

The high-efficiency solid-liquid separation unit has a hydraulic retention time of approximately 9 minutes, plus the mixing from the preceding pump and pipelines, resulting in a total hydraulic retention time of less than 10 minutes, significantly shorter than that required by traditional treatment processes. With such a short treatment duration, the turbidity of the effluent meets the industrial reuse water quality standards. Moreover, the amount of inorganic flocculant required is lower than that in traditional flocculation and sedimentation processes.

(2) The separated sludge has a low moisture content, eliminating the need for specialized concentration treatment. The high-efficiency solid-liquid separation unit boasts excellent dewatering performance for the sludge, reducing its moisture content to below 85% after staying in the sludge storage area for over 1 hour, allowing for final sludge treatment without specialized concentration.

(3) Highly adaptable with versatile processing capabilities, the efficient solid-liquid separation unit not only handles continuous wastewater treatment but also intermittent treatment. It boasts strong resistance to shock loads, ensuring water quality treatment even when exceeding the rated load by 50%.

Below, we use the application of fluidized bed technology in the reuse of car wash wastewater treatment as an example to introduce the use of fluidized beds in industrial wastewater treatment: In response to the current situation of water pollution and waste in the car washing industry, various car wash wastewater reuse equipment have emerged on the Chinese market in recent years.

Some utilize multi-media filters, granular activated carbon filters, and ultra-filtration systems, employing principles of retention, adsorption, and sieving to treat and reuse wash water; others adopt conventional oil separation, sedimentation, filtration, and disinfection methods.

Although the effluent processed by these equipment meets the water quality standards for car washing wastewater, their common drawbacks are large land occupation and high construction and operation costs, which have posed many difficulties in entering the technical release market.

However, when treating car wash wastewater using granular fluidized bed technology, the effluent quality after processing through the fluidized bed unit can meet the standards for car wash recycling water. The sludge produced by the granular fluidized bed method has a significantly lower moisture content compared to that produced by conventional coagulation and sedimentation methods, eliminating the need for sludge concentration equipment.

Additionally, compared to traditional treatment processes, the granular fluidized bed method boasts advantages such as a smaller land footprint, simpler equipment structure, and lower investment and operating costs. Therefore, its application in the reuse treatment of car wash wastewater presents a promising market前景.

5. Industry Outlook

During the implementation of the "National Ecological Environment Construction Plan," the comprehensive utilization of water resources, water recycling, and water pollution treatment are particularly critical components. As a result, the market capacity for water treatment equipment will significantly increase, with market competition focusing on technological level, applicability, and pricing.

The series of geotextile equipment using this technology boasts features like advanced technology, compact size, and low cost, and can be produced according to customer specifications, positioning it as a strong competitor in the environmental protection equipment market.

The primary users of the equipment will be small and medium-sized industrial enterprises for industrial water treatment, wastewater treatment, industrial water recycling, as well as urban small and medium-sized water supply treatment and sewage plant sludge treatment.