Recently, a number of phosphogypsum acid co-production clinker projects have been disclosed on the Internet. The total amount of co-production clinker projects is estimated to be millions of tons. In the current market environment, it has attracted the attention of many cement practitioners. Many people will be curious that phosphogypsum itself is a pile of waste residue. At present, cement retarder is mainly used in cement industry. How can sulfuric acid and cement be produced?
In fact, the technology of phosphogypsum acid co-production cement has existed for a long time. The earliest one in China should be a chemical enterprise in Shandong Province. Because of the high cost and other reasons, it has not been widely promoted. At present, the process has been upgraded to the third generation process, and the cost has been further reduced. Recently, the price of sulfur has soared due to various factors, which has caused the price of sulfuric acid to soar; In terms of economic benefits, the main product of phosphogypsum acid co-production clinker project is sulfuric acid, clinker as a by-product, simply calculating the economic account of clinker products is estimated to be more expensive than cost of ordinary clinker, but the comprehensive account has a higher rate of return according to the current market price of sulfuric acid, which is the core of the recent phosphogypsum acid co-production clinker project. The following is a simple popular science from the perspective of production process, which is called "sulfur-calcium double cycle" production process.
1. Core principle: split phosphogypsum into two products
. The main component of phosphogypsum is calcium sulfate dihydrate (CaSO.2HO). In the traditional utilization of phosphogypsum, only the calcium element is used and the sulfur element is lost. The process of co-production of phosphogypsum acid and clinker is to "eat up and squeeze out" these two elements.
Its core chemical reaction can be summarized as:
CaSO.2HO + C + SiO₂ → CaSiO (cement clinker) + so ↑ + CO ↑ + HO ↑
. Decompose the calcium sulfate in phosphogypsum:
• Sulfur element: turn into sulfur dioxide (SOSO) gas, which is collected, purified, converted and absorbed to produce high-concentration industrial sulfuric acid. The sulfuric acid can be directly sent back to the phosphoric acid production plant and reused for phosphate rock extraction to realize the internal circulation of sulfur resources.
• Calcium element: calcium oxide (CaO) produced by decomposition reacts with silicon, aluminum, iron and other elements in the ingredients and is sintered into cement clinker. These products enter the building materials market to realize the high-value utilization of calcium resources.
2. Process flow: five-step transformation
from waste residue to product. A complete set of phosphogypsum acid-making co-production line usually includes the following five core links:
1. Raw material pretreatment: phosphogypsum is first filtered and dried to remove free water and crystal water. Become anhydrous calcium sulfate, which is convenient for subsequent batching.
2. raw material preparation: mix that dehydrated phosphogypsum with coke (reduce agent), siliceous raw material, aluminous raw material, ferruginous raw material and the like according to a precise proportion, and grinding into raw material powder. 3.
high-temperature calcination: the raw material powder is sent into a special preheater for preheating, and then enters a rotary kiln for reduction calcination at the high temperature of 1200-1300 deg C. This is the core of the whole process, where phosphogypsum is decomposed. The specifications and models of rotary kilns of a project in Guizhou are as follows: 2 sets
of Φ5.58 × 110m rotary kilns. 4. Flue gas acid production: The high-temperature flue gas containing SO2 produced at the kiln tail is purified, dedusted and dried, and then sent to the sulfuric acid plant to produce industrial sulfuric acid through the "double conversion and double absorption" process.
5. Clinker cooling and processing: The high-temperature clinker produced by the kiln head, after being cooled by the grate cooler, is qualified cement clinker (some items are called silicate admixture), which can be sold directly or further ground into cement.
On the whole, the clinker manufacturing process of the phosphogypsum acid co-production clinker project is very close to the ordinary new dry clinker production process, and many of the equipment used are general equipment in the cement industry.
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