Moisture management in vertical roller mills
Disclosed are exemplary method and system for manufacturing cement in a vertical roller mill (VRM) using humidity sensor readings. This enables adjustment of operational variables such as material feed, water, grinding additives, air flow, temperature, and their combinations. Exemplary embodiments allow manufacturers to predict and to improve cement properties, such as strength and setting time, by monitoring and managing humidity of air in the VRM and/or its air flow system.
1. A system for manufacture of cement, comprising:
(A) a vertical roller mill comprising:
a grinding table for grinding particles comprising clinker and a sulfate source chosen from gypsum, plaster, calcium anhydrite, or a blend thereof;
at least one rotatable roller for providing rolling contact with the grinding table to grind the particles;
a classifier for removing ground particles from the vertical roller mill;
an air flow system to carry particles from the grinding table through the classifier; and
at least one dispenser apparatus for introducing water, cement grinding aid, or both, to contact the particles;
(B) at least one humidity sensor that provides a humidity output corresponding to a moisture level of air inside the vertical roller mill or the air flow system;
(C) a processor for comparing the humidity output from the at least one humidity sensor with at least one selected from the group consisting of
(i) a predetermined humidity threshold level or at least one pre-established relationship between relative humidity and one or more cement property of interest, wherein the predetermined humidity threshold level and the at least one pre-established relationship is selected based on correlations between the humidity output and one or more physical or chemical properties of the corresponding finished cement, hydrated cement, or cementitious product made with the cement;
(ii) at least one data set or mathematical relationship that contains correlations between the humidity sensor output and one or more physical or chemical properties of the corresponding finished cement, hydrated cement, or cementitious product made with the cement; and
(iii) both (i) and (ii), wherein
the processor is programmed to initiate, based on the comparison, at least one protocol chosen from: (i) providing a visual or auditory alarm; (ii) adjusting water, cement grinding aid, or both being dispensed onto the grinding table or the particles ground on the grinding table; (iii) adjusting air flow entering or exiting the vertical roller mill or the air flow system; (iv) adjusting temperature of air inside the vertical roller mill or air flow system; (v) adjusting amount of materials introduced into the vertical roller mill; or (vi) a combination thereof.
2. The system of claim 1 further comprising, a vibration sensor that senses vibration of the vertical roller mill and provides a vibration output indicative of vibration level.
3. The system of claim 2 , wherein the processor receives the humidity output from the at least one humidity sensor, and, based on comparing the humidity output from the at least one humidity sensor with a predetermined humidity threshold level or dataset, initiates a protocol whereby water amounts introduced into the vertical roller mill or onto the particles being ground in the vertical roller mill are reduced, while cement grinding aid amounts introduced into the vertical roller mill or onto the particles being ground in the vertical roller mill are increased, and/or the grinding aid composition is changed.
4. The system of claim 3 , wherein the processor receives the humidity output from the at least one humidity sensor and initiates adjustments to water level and cement grinding aid amount dispensed into the vertical roller mill, said adjustment being limited by a vibration level limit or pre-determined maximum value.
5. The system of claim 1 , wherein the processor receives the humidity output from the at least one humidity sensor and compares the humidity output to a predetermined humidity threshold level or dataset at successive intervals of no greater than every 60 minutes.
6. The system of claim 1 , wherein the one or more physical or chemical properties are chosen from pre-hydration level, compressive strength, initial setting time, final setting time, slump, slump retention, workability, and flowability of the finished cement, hydrated cement, or cementitious product made using the cement.
7. The system of claim 1 , wherein the at least one humidity sensor monitors humidity level of air flow exiting from the air flow system through an exhaust chimney.
8. The system of claim 1 , wherein the at least one humidity sensor is located within the vertical roller mill.
9. The system of claim 1 , wherein the at least one humidity sensor is positioned in the air flow system of the vertical roller mill.
10. The system of claim 1 , wherein the at least one humidity sensor is configured to provide a relative humidity output corresponding to relative humidity values, and the relative humidity values are outputted directly from the at least one humidity sensor or calculated by the processor based on absolute moisture concentration in the air, temperature of the air, dew point of the air, or a combination thereof.
11. The system of claim 1 , wherein the processor compares the humidity output from the at least one humidity sensor with the at least one data set or mathematical relationship that contains correlations between the humidity output and compressive strength of hydrated cement or cementitious product cured to a specific age.
12. The system of claim 1 , wherein the processor compares the humidity output from the at least one humidity sensor with at least one data set or mathematical relationship that contains correlations between humidity sensor output and initial set time or final set time of hydrated cement or cementitious product.
13. The system of claim 1 , wherein the processor receives the humidity output from the at least one humidity sensor, and, based on comparing the humidity output from the at least one humidity sensor with the predetermined humidity threshold level or dataset, initiates a protocol whereby the air temperature inside of the mill is modified by adjusting the fresh air, hot gas, recirculation, chimney damper, hot gas generator fuel consumption rate, speed of hot gas generator fan, or a combination thereof.
14. The system of claim 1 , wherein the processor receives the humidity output from the at least one humidity sensor, and, based on comparing the humidity output from the at least one humidity sensor with a predetermined humidity threshold level or dataset, initiates a protocol whereby the amount of fresh air entering the mill is modified by adjusting the fresh air, recirculation, chimney, hot gas damper, speed of the hot gas generator fan, or a combination of any of the foregoing.
15. The system of claim 1 , wherein the processor receives the humidity output from the at least one humidity sensor, and, based on comparing the humidity output from the at least one humidity sensor with the predetermined humidity threshold level or dataset, initiates a protocol whereby the amount of total feed, the proportion of clinker to secondary cementitious materials, or the sulfate level is adjusted, or any combination thereof.
16. The system of claim 1 wherein the processor receives output from the at least one humidity sensor and compares the output to a predetermined humidity threshold level or dataset at successive intervals of no greater than every 60 seconds.