Describes the combination sculls leaves and tray drying system drying processes, the device structure and working principle, the energy consumption of its good use and environmental resistance were analyzed and compared, it affirmed this combination compared to conventional drying system flash convective drying compositions in the industrial production of barium salt rationality and significant energy savings.

 

BaSO4 as colorless orthorhombic crystals or amorphous white powder, non-toxic, decomposed at 1450 ℃. Chemically stable, very low solubility in water (60 ℃ when the maximum solubility in water, of 0.46g / 100g water), mainly used in paint filling. In the process of barium sulfate, the drying step is the last one, at present China has a variety of commonly used drying method, a rotary flash drying, two pairs of blades drying, rotary drying kiln dried and paddles leaves dried combination disc plus its dry mode of production is directly related to the quality of the final product, the impact of the final product moisture content, whiteness and other technical indicators. We design and manufacture and installation of a company's annual output of 40,000 t precipitated barium sulfate (22,000 tons by-product sodium sulfide) system that uses a combination disc plus paddles leaves drying system, barium sulfate slurry moisture content of about 25%. material white paste; after the final moisture content of dried material should reach 0.2%, an apparent density of 3.5 ~ 3.8Kg / L.

 

1, process and equipment

1.1 selection process
Barium sulfate slurry from the wet material is dried to a moisture content of 25% to 10% of water in the process, there is then a matter of gradually hardens and becomes loose sticky process; select paddles leaves this dryer is suitable for physical changes. 10% water and loose material flow is good, the choice of a tray dryer. Therefore, using a combination of dry first double disc blades again in the project, double-blade and tray dryers are of conduction dryer. After the process step by former horizontal spiral centrifuge separation water content of about 25% of the wet material into the first dryer paddles leaves, pre-dried to a moisture content of about 10%, after the material portion viscous loose granular powder was removed, and then proceeds to carry out the drying operation (process shown in Figure 1), to reach the final product moisture requirements within a tray dryer.

 

1.2 paddles leaves Dryer
Paddles leaves the dryer is conduction dryers. By the body shell jacket, the double helix drying conveyor shaft drive mechanism, roof, exhaust systems and other components. A heated twin screw conveyor dryer horizontal work within the housing jacket and a drying conveyor shaft through the 0.6MPa steam, wet material from the dryer on the top cover of the dryer feed port was added, turning the dry transfer shaft driven by the continued roll forward the material to complete the heat drying operation during movement; the bottom of the dryer after the drying is done by the other end of the discharge port and simultaneously to complete the transfer process.

 

1.3 paddles leaves Dryer Features
⑴ paddles leaves the dryer handle a wide range of materials, using different heat medium that can handle paste, granular, powdery material, can handle heat-sensitive materials, but also require high temperature processing of materials processing; ⑵ entire drying process closed operation stirring, mixing process, to turning violent material, material particles full contact with the heat transfer surface in the axial zone, material temperature, humidity, mixing gradient is very small, so as to ensure the stability of the process; but also access a higher heat transfer coefficient, heat transfer coefficient generally can be reached 80-350W / (m • K); ⑶ paddles leaves dryer indirect heating material, not a lot of air to carry heat away relatively low energy consumption; ⑷ dryer the released water vapor directly from the material discharged from the top of the drier exhaust pipe, the exhaust steam is the main component, the gas velocity is low, less dust, there is no entrainment of the dried product; environmental pollution, while reducing the dust recovery equipment investment; ⑸ paddles leaves the dryer can also be a continuous operation intermittent operation, low speed agitation and reasonable structure. A small amount of wear, maintenance costs low.

 

1.4 tray dryer
Disc continuous drying machine is a new conduction drying equipment, disc continuous dryer vertical work by drying trays, rake arm, mounted in several rake leaves rake arm, spindle, gear, housing and other components; wet materials are added from the top of the charging port, through the HTF 250 ℃ within the hollow drying trays. Drying trays and small cap market is divided into two types, horizontal layer in a dryer-style layout, dried stationary plate, the material on the market movement from outside to inside in rake leaves, driven from the inside edge of the small cap market's fall inside edge of the material on the small-cap movement from the inside out, from the outer edge of falling into the small-cap market, in the dry material is conveyed by the disk rake leaves, turning, it was Archimedes spiral trajectory, in the course of the campaign heated drying pan, heat transfer and mass transfer to complete the drying process by drying after-hours each discharged from the bottom of the dryer, the entire drying process closed operation, the release of water vapor from the material through the pulse jet bag filter dust after emissions from the induced draft fan to the atmosphere.

 

1.5 disc dryer Features
⑴ heating disc, the material is slowly pushing rake leaves, small mutual abrasion between material, shape before and after drying the material, the size of small changes, breakage rate is very low, the quality of the crystal surface of the material will have little impact ; ⑵ material temperature control is accurate, easy to residence time of materials can be accurately adjusted; ⑶ material flows single, no back-mixing, even drying and stable quality, no re-mixing; ⑷ continuous disc dryer its configuration is simple, not must be equipped with air-drying configured cyclone, do not use hot air as the heating medium, therefore, the product losses due to poor separation of hot air and dust entrained with the exhaust caused not occur; continuous operation, closed operation, high evaporation intensity, humidity gradient distribution reasonable, low power consumption, small footprint;

 

1.6 Equipment Selection
Since BaSO4 products of iron ions, there are strict requirements, so paddles leaves dryers and tray dryers contact material part 0Cr18Ni9 stainless steel; its facilities such as dust removal equipment, in order not to affect the quality of the product recovery section, also use stainless steel 0Cr18Ni9 material.

 

2, equipment performance and operating parameters
2.1 device performance parameters (Table 1)

 

Table 1 20000t annual output of barium sulfate two dryer performance parameters

project parameter	A leaf Sculls Dryer	Two disc Dryer
Dryer Specifications	60m2	GDPG2500/14C
Heat transfer medium	Steam	HTF
Consumption (steam / bituminous coal)	2.5t/h	130Kg / hr
Drying area (square meters)	60㎡	60㎡
Spindle speed(rad/min)	15	1~9
Motor Power(kw)	55	7.5

 

2.2 equipment operating parameters (Table 2)

 

Table 2 barium sulfate production operating parameters

project parameter	A leaf Sculls Dryer	Two disc Dryer
The initial moisture content of barium sulfate(%)	25%	9%
Capacity(t/h)	3.74	3.08
Annual capacity (million t / Year)	2.68	2.22
The initial temperature of the material℃	20	80
Drying temperature of the material inside the machine℃	80	100
Heat transfer medium temperature（℃）	160℃	250℃
After drying the moisture content of the product%	9%	0.2%
After drying semi-finished and finished products(t/h)	3.08	2.8
Semi-finished and finished products (million t / Year)	4.43	2.02

 

　　

The paddles leaves dryers and tray dryers combination of barium sulfate is dried, full and effective use of their respective advantages, sculls leaves drier effective solution of barium wet sticky and difficult to deal with the problem; tray drying machine effectively solve the water problem in depth the effect of drying below 10%, the combined system in the industrialized good practical effect of the production process.

Double disc blades plus a combination of dry and drying system flash drying system compared to the same yield and production conditions, combined drying system can save 30% -40%, but double disc blades dry composition plus the cost of partial drying system high; compared to the double disc blades plus dry composition drying system and two pairs of blade drying system, which is higher cost and power consumption; double disc blades plus dry composition drying system compared with the rotary drying kiln, the latter the system covers a larger investment is high, and the whiteness of the product is not guaranteed.