Since April this year, two sets of gasified water-cooled high-efficiency cement coolers (hereinafter referred to as coolers), researched and manufactured by Shanxi Longzhou Conveying Machinery Co., Ltd., have been put into operation in Leshan, Sichuan and Tangshan, Hebei respectively.
The unit in Leshan, Sichuan achieves a capacity of 220 t/h. The initial cement temperature is about 85℃, the inlet water temperature around 30℃, with a temperature drop of 25～30℃.
The unit in Tangshan, Hebei runs at approximately 400 t/h. The initial cement temperature is 120℃, inlet water temperature about 30℃, delivering a temperature reduction of 28~32℃. Both projects have obtained satisfactory results from customers.
The second cooler ordered by the Tangshan customer is ready for shipment. Another cooler purchased by a special cement company in Sichuan is under fabrication. Many clients have inquired about detailed information of our coolers.
What points should be considered when selecting a cement cooler? Here we give a brief introduction.
When selecting a cooler, the operating parameters must be clarified: hourly throughput, initial cement temperature, inlet water temperature and required temperature drop.
The technical standard for our coolers is as follows: for initial cement temperature below 100℃ and inlet water temperature under 30℃, the temperature drop is 25℃; for initial cement temperature above 100℃ and inlet water temperature under 30℃, the temperature drop is 30℃.
Customer requirements may differ from this standard. Some require a lower temperature drop, while others need a higher one, and the deviation can be significant. Therefore, equipment selection and cooling water configuration shall be carried out according to customer requirements to meet diverse demands.
Thanks to superior technical performance of the vertical structure of the cooler, the vertical type is generally adopted when site conditions permit.
The gasification state of cement inside the cooler enables horizontal inlet and outlet of material. Therefore, the optimal installation position for the cooler is on the side of the trestle where the air slide is installed, in an area that will not obstruct walkways and other facilities, or other elevated locations. The bottom of the cooler is mounted on the ground via a steel frame, while the top inlet and outlet connect to the main air slide or other equipment.
When installing the cooler on the bypass of the air slide, if the process drop of the air slide for material in and out of the cooler is insufficient, the air slide before the cooler can be raised, or the main air slide after the cooler can be lowered. This ensures smooth material flow from the main air slide into and out of the cooler through short air slides.
The advantage of this process: material flows through the cooler via the bypass when the cooler is in service; when the cooler is not in use, the main air slide conveys material directly to downstream equipment.
Recently, during a site visit to an enterprise in southern China, the customer raised a requirement: the volume of low-temperature cement needed is relatively small. Is it feasible to install the cooler under the cement silo for bulk storage? When low-temperature cement is required, cement discharged from the silo enters the cooler, and after cooling, returns to the inlet of the bulk loader for loading. We have proposed a process solution according to site conditions and are waiting for technical personnel of the company to approve the proposal.
Whether the cement grinding system adopts an open circuit or closed circuit has a significant impact on cooler selection. In an open-circuit process, cement temperature is high, generally above 100℃, and the required temperature drop is usually over 30℃. Special structures are required for larger temperature drops. Cement contains a small amount of metallic particles. A deslagger is preferably installed upstream of the cooler to remove these particles. Otherwise, such particles tend to accumulate at the bottom of the cooler housing. Once accumulated to a certain level, they will raise the pressure of the Roots blower, trigger tripping shutdown, impair cooling performance or even cause equipment outage.
Cement produced by the closed-circuit process has a lower temperature compared with that from the open-circuit process. Due to the lower initial cement temperature, the temperature difference between cement and cooling water is small, making temperature reduction more difficult than in the open-circuit system. The normal temperature drop is 25℃.
If a higher temperature reduction is required, it shall be specially specified, and additional technical measures will be adopted to guarantee the performance.
Hardly any metallic particles exist in cement from the closed-circuit process. Only condensed lumps occasionally peel off from the inner walls of elevators, chutes, pipelines or conveyors. In principle, deslagging equipment is not required. Nevertheless, installation of such equipment is preferable.
The overflow process, determined by the inherent structure of the cement cooler, keeps the cooler body fully filled with cement during shutdown or restart. For single-variety production, the cement inside the cooler is renewed through displacement, with new cement replacing the old, so cement quality remains unchanged. However, when switching to a new cement variety, the new cement will mix with the original cement retained in the cooler. This results in uncontrollable quality fluctuations during the transition phase between the two cement grades and may easily trigger quality nonconformities.
Therefore, when a cooler is used in a cement process requiring product variety change, the residual cement retained inside the cooler must be emptied before the completion of production of the previous cement grade. Before switching varieties, the three-way valve feeding the cooler shall be closed and the direct cement passage (chute and conveying equipment) opened. The residual cement inside the cooler is lifted into the direct passage by the elevator equipment.
Regarding the optimal device for lifting residual cement inside the cooler, we consider an airtight feed pump to be the better option. The reasons are as follows:
1. A bucket elevator comes with high equipment cost, complex structure and large footprint. Despite its low power consumption during operation, the volume of residual cement in the cooler is small and can generally be emptied within half an hour. It is uneconomical to deploy a large, high-value bucket elevator for this short operation.
2. High-pressure pneumatic conveying equipment such as tank pumps is more expensive than low-pressure airtight feed pumps for short lifting and conveying distances, and it requires a large supply of high-pressure gas to maintain operation.
3. Low-pressure pneumatic conveying equipment adopts either airtight feed or rotary mechanical sealing structures. After the cooler has been in operation for a period, a certain amount of metallic particles will accumulate inside it. These particles may jam the rotary machinery and result in mechanical failures. A Roots blower for fluidization is already installed under the cooler, whose parameters fully match or slightly exceed those required by the airtight feed pump. Therefore, the airtight feed pump is a favourable option for emptying the cooler.
Due to space constraints, the process for two grinding systems sharing one cement cooler will be described in subsequent sections.
If you have any questions regarding cement cooling, please feel free to contact us.
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