The limestone gypsum (wet) desulfurization process is currently the most widely used and mature desulfurization technology in the world, with a desulfurization efficiency of over 95%. However, while this desulfurization process effectively reduces sulfurization pollution, it also generates a large amount of industrial waste - desulfurization gypsum. This industrial by-product with high grade and a content of over 90% calcium sulfate dihydrate (CaSO4 · 2H2O) is only a high water content industrial semi-finished product before secondary processing. It is piled up in large quantities, occupying land and wasting resources. The acidic and other harmful substances it contains can easily pollute the surrounding environment, seriously restricting the development of wet flue gas desulfurization technology.
Therefore, driven by the circular economy, using desulfurization gypsum as raw material to produce high-quality gypsum based on its characteristics has become an effective way to solve the problem of secondary pollution caused by desulfurization slag, thus achieving a magnificent transformation from industrial waste to the rising star of building materials.
At present, desulfurization gypsum is mainly used in the production of gypsum blocks, paper faced gypsum boards, putty gypsum, plastering gypsum, high-strength gypsum, cement retarders, and soil amendments in various countries around the world. Today we will take a detailed look at the deformation history of desulfurization gypsum!
Desulfurized gypsum vs. natural gypsum
Desulfurized gypsum, also known as flue gas desulfurization gypsum, sulfur gypsum, or FGD gypsum, is an industrial by-product obtained by desulfurizing and purifying the flue gas produced after the combustion of sulfur-containing fuels (mainly coal).
gypsum
The main mineral phase of desulfurization gypsum is calcium sulfate dihydrate (CaSO4 · 2H2O), and the main impurities are related minerals associated with limestone (such as calcium carbonate, alumina and silica, iron oxide, calcite, feldspar, calcite, etc.). Its physical appearance, particle size and grading, moisture content, and impurity composition are different from natural gypsum, but these do not affect its building performance.
Desulfurization Gypsum
Especially in terms of physical and chemical properties, desulfurization gypsum is basically the same as natural gypsum. The hydration kinetics, coagulation characteristics, and process of desulfurization gypsum are the same as natural gypsum, but the speed is faster; At the same time, the grade of dihydrate gypsum (CaSO4 · 2H2O) in desulfurization gypsum is as high as (90-93)%, with a free water content of 10% -12%, low alkali content, no radioactivity, and few harmful impurities. Therefore, it has become the main industrial raw material for replacing natural gypsum and producing gypsum building materials.
Currently, the country with the best application of desulfurization gypsum in the world is Japan, followed by European countries such as Germany and France. The technology and equipment for calcination and deep processing of desulfurization gypsum in China are gradually maturing, and the application of desulfurization gypsum is in a very rapid development stage. The Yangtze River Delta, which does not have natural gypsum resources but has a large amount of desulfurized gypsum, has developed the fastest. Shanghai, Zhejiang, Jiangsu and other places have many newly built large-scale paper faced gypsum board production lines using desulfurized gypsum as raw material. The comprehensive utilization of desulfurization gypsum is also flourishing in the Beijing Tianjin Hebei region and the Pearl River Delta region.
The main applications of gypsum building materials
Gypsum building materials mainly made of desulfurization gypsum are a multifunctional gas hardening cementitious material, which is dehydrated from dihydrate gypsum (CaSO4 · 2H2O) at different temperatures and pressures.
Under normal pressure drying conditions, gypsum dihydrate is dehydrated to form β - CaSO4 · 1/2H2O when heated to 120 ℃~140 ℃, β - CaSO4 Ⅲ when dehydrated to 170 ℃~190 ℃, CaSO4 Ⅱ - s and CaSO4 Ⅱ - u when heated to 320 ℃~360 ℃, and CaSO4 Ⅰ when heated to 400 ℃~700 ℃; Heating to 150 ℃~160 ℃ in liquid or under vapor pressure dehydrates to form α - CaSO4 · 1/2H2O.
β - CaSO4 · 1/2H2O is the main component of building gypsum, used in the production of various building materials gypsum products. CaSO4 II-s is mainly used in the production of plastering gypsum, and α - CaSO4 · 1/2H2O is mainly used in the production of model gypsum.
Gypsum building materials have low energy consumption in production, and the products have the advantages of light weight, fire resistance, sound insulation, adjustable indoor air humidity, and convenient construction. There is no harmful gas release during long-term use, making it a typical "green building material".
1. Paper faced gypsum board
One of the main applications of gypsum building materials is paper faced gypsum board.
Paper faced gypsum board is a lightweight building sheet made mainly from building gypsum and protective cardboard, mixed with appropriate amounts of fibers, starch, accelerators, foaming agents, and water, and processed through mixing, molding, solidification, cutting, drying, and edge cutting. It can be widely used in various industrial and civil buildings, especially in high-rise buildings, as interior wall materials and decorative materials. It has the advantages of light weight, fire resistance, earthquake resistance, thermal insulation, good processing performance, convenient construction, good disassembly and assembly performance, good decorative effect, and increased usage area.
The mainstream development trend of paper faced gypsum board production lines in China is towards large-scale production and the use of chemical gypsum as raw material.
Gypsum board Production line
The large-scale paper faced gypsum board production line adopts the most advanced production technology and equipment at home and abroad, with a series of advantages such as excellent and stable product quality, fast production line speed and high output, high automation level with fewer operators, reduced energy consumption per unit area with less pollution emissions, low construction cost per unit area, and less land occupation. In recent years, the number of newly constructed factories in China has mostly reached 30 million square meters per year. And the single line production abroad is 70 million m ²/a.
Before 2004, the production of paper faced gypsum board mainly used natural gypsum as raw material, mostly distributed in areas with abundant natural gypsum mineral resources. With the continuous development of desulfurization gypsum treatment technology and equipment, as well as the surge in desulfurization gypsum volume, new paper faced gypsum board production lines built after 2006 mainly use desulfurization gypsum as raw material. Some old factories have also carried out raw material transformation, transforming natural gypsum treatment systems into desulfurization gypsum treatment systems.
Riding on the trend of industry upgrading, Jason Company, which stands at the forefront of the industry, set up its first gypsum board production line using desulfurization gypsum as raw material in Jiaxing, Zhejiang in 2007. Since then, it has added three other 30 million m ²/a gypsum board production lines in Huizhou, Jiaxing, and Changchun, radiating to the Yangtze River Delta, Pearl River Delta, Beijing Tianjin Hebei, and Northeast regions. Currently, its comprehensive production capacity has reached 120 million m ², and its products cover the full range of national standards. During this period, Jason Company was also promoted and reported by CCTV as a representative enterprise for comprehensive resource utilization, energy conservation, and emission reduction, receiving widespread attention from the industry.
2. Painting gypsum
Gypsum plastering is a multiphase gypsum binder with various properties required for plastering materials: fast initial setting, slow final setting, suitable for the average working speed of plasterers; Has flexibility and plasticity, with high pulp production; The plaster layer dries quickly, has suitable bulk density, and high strength.
Gypsum plastering is an efficient and energy-saving material for plastering interior walls and ceilings of buildings. It mainly replaces building cement, lime and mortar plastering. Traditional cement mortar and mixed mortar have disadvantages such as easy cracking, hollowing, excessive ash on the ground, slow setting and hardening, and long decoration cycle. Gypsum plastering can completely overcome these disadvantages and is the development direction of plastering materials.
Lime mortar and cement mortar have been basically eliminated in developed countries abroad, and now plaster gypsum is used for wall and roof plastering. For example, in Germany, indoor plastering with plaster accounts for 80% of the total plastering volume, with an annual usage of 4 million tons; Gypsum plastering has formed a relatively complete industrial system, providing one-stop services for production, supply, and marketing. The factory directly transports bulk gypsum plastering to the construction site, and then uses a spraying machine to spray the wall, smooth and polish it. The development trend is good.
The market potential for plastering gypsum in China is enormous. Currently, 1.5 billion square meters of new urban residential buildings are built annually across the country, and 1400 square meters (2700t) of cement mortar are required for every 10000 square meters of construction. The addition of interior walls and ceilings accounts for nearly 70% of the mortar required for painting and masonry of the entire building. The interior walls of a 1.5 billion square meter building also require 255 million tons of plastering mortar, calculated at a ratio of gypsum to material of 1:3. If all gypsum is used, 63 million tons can be used.
In addition, gypsum building materials can be cast to produce gypsum partition blocks, which are mainly used for non load bearing internal partitions and are very suitable for application in urban buildings.
Various signs indicate that the acceleration of China's urbanization process has put the production of gypsum building materials on a rapid development track, and the large-scale resource utilization of industrial gypsum will accelerate this development pace.
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Reprinted: China Construction Research Institute Gypsum Industry Branch
