A cement plant in Gujarat (India), partnered with Ecomak Systems to improve production capacity by 1 Million TPA by implementing the Reverse Air Baghouse design by Ecomak.
by Ecomak Systems
Introduction
Gujarat is a state in the western part of India with beautiful coastal beaches, as well as good quality of limestone reserves. A reputed company installed a single stream cement plant, with a capacity of 2 million TPA, in the Kutch district of Gujarat in 2002. At the time of installation, the plant had the highest capacity for single kiln. The plant was set up in the collaboration with M/s Fuller USA and its Indian associate Fuller KCP. In 2006, the plant was modernised and the capacity was increased to 2.6 million TPA. This was steadily increased to 3 million TPA (9100 TPA) till 2016.
The raw mill section mainly consists of a gas conditioning tower, cyclones, a reverse air bag house, a vertical roller mill, an exhaust fan, and a stack. The reverse air bag house, which has fiberglass bags was used for filtering the kiln and raw mill gases. The bag house works either with or without the vertical roller mill. The dust laden gas from the preheater either travels to the raw mill or to the baghouse after gas conditioning or dilution. The exhaust gas from the raw mill is passed through the bag filter after a set of cylones and the raw mill fan. The bag filter therefore receives the dust laden gas either directly from the preheater, or from the roller mill. The ID fan exhausts the clean gas from the bag filter. The process filter data and the technical specifications are given in Table 1.
As the plant capacity was increased, the differential pressure across the bag house became a serious issue and led to the frequent failure of the filter bags, as well as reduced bag life. The electrical consumption was also higher due to the high-pressure differential across the bag house. After facing the problem for a prolonged period, the cement manufacturer decided to revamp the existing bag house to rectify the issues, and floated the enquiry for modification of the present baghouse in 2016. After various rounds of discussion and facing various strong competitors, Ecomak Systems Private Limited won the contract to design, manufacture, revamp and commission the bag house in May 2016. The main issues stressed by Ecomak were as follows:
- The number of filter bags and the filter bag dimensions were maintained. There is no need to change the bag height. This essentially means the filter area will not be changed.
- Various gas sections to be redesigned to ensure optimum gas velocities for revised gas flow conditions to achieve low pressure drop.
- The size of the dampers and the number of the dampers will be resized for excessive flow.
The project was treated as a fast track project, and erection and commissioning was to be completed within 30 days, during the planned annual shut down of the cement plant.
The following issues were considered for the improvement in the present bag house:
- The dust emission level should be maintained or improved
- The pressure differential across the bag house should be improved
- The overall energy cost should be lower
- The frequency of the bag failure should be reduced
- The life of the filter bags should increase
Technical Solution
The aim of redesigning the bag house was to reduce the pressure differential upto 170mm WG or below across the bag house to suit the increased gas flow rate. There was no scope to increase the number of modules, or number of bags per module due to site constraints. On one side of the baghouse there is a conditioning tower, and on the other side an existing fan is installed, along with a stack.
The total pressure drop across the baghouse consists of the pressure drop across the filter media, as well as the mechanical pressure drop. After detailed analysis, it was observed that the gas velocities in the various sections were very high. It was decided to reduce the mechanical pressure drop by various measures, as follows.
- Redesign the gas inlet cross-sectional area. This is to reduce gas velocity in the inlet zone
- Redesign the number of dampers for each module. The damper size was also increased. This helped to reduce the gas velocities across these dampers.
- Redesign the number of outlet poppet dampers for each module. The damper size was also increased. This helped to reduce gas velocity across the dampers
- Redesign the gas outlet cross sectional area. This is to reduce the gas velocity in the outlet zone
The dust discharge system was maintained without any change. Suitable changes were made in the plant PLC to suit the above changes. All the above changes were carried out, taking into account the various constraints of the existing baghouse dimensions.
The cement producer has changed the filter bags in some compartments from the fiber glass with treatment, to fiber glass with Teflon membrane, and is planning to change those in the remaining compartments in a phased manner. This will ensure long bag life as well as reducing pressure drop across the filter media. The smooth surface of the Teflon membrane aids quick and easy dust separation from the filter surface, and reduces the dust thickness on the filter surface. This helps to reduce the pressure drop across the filter media. Due to heavy corrosion, certain bag house walls were also replaced with new walls. In certain compartments, the tube sheets and thimbles were also replaced.
| Parameters | Original bag house specifications (2 million TPA capacity) | Revised bag house specifications (3 million TPA capacity) |
| Gas Volume | 1.25 million m3/hr during raw mill running 1.28 million m3/hr during raw mill shutdown | 1.8 m3/hr |
| Gas Temperature | 260 deg C max | 260 deg C max |
| Dust Load | 65 g/m3 max | 65 g/m3 max |
| Dust Emission | 50 mg/Nm3 | 50 mg/Nm3 |
| Number of compartments | 22 | 22 |
| Bags per compartment | 242 | 242 |
| Filter Area | 50464 m3 | 50464 m3 |
| Filter media | Fiberglass with silicon, graphite, and Teflon treatment | Mixture of fiberglass with treatment, as well as Teflon membrane |
| Pressure differential across bag house | 150-180 mm WG | 260-280 mm WG |
| Bag dimensions | 292 mm dia. X 10338 mm height | 292 mm dia. X 10338 mm height |
Assembly and Commissioning
Effective communication between the supplier and the purchaser is extremely important for smooth execution of the project. Regular monitoring of the project’s progress prevented delays, enabling the revamped bag house to be commissioned on time. To achieve the guaranteed and flawless operation of all filter components, specialists carried out the commissioning of the filter plant. The company not only provided the optimum technical solutions, but also completed the project as scheduled.
Erection and the commissioning activity was completed in about 30 days, and was commissioned by August 2016. The project was completed on a fast track basis, with an excellent support from the customer.
The plant went on stream to operate smoothly. After testing the preheater at full load, the performance was demonstrated to the customer. The pressure drop observed across the bag house was in the range of 120-130 mm WG, against the targeted figure of 170 mm WG. The actual performance exceeded the target value and the client was extremely happy. Since commissioning, the client has not faced any problems due to the modification of the bag house and is enjoying the full benefits of the low pressure drop, leading to lower power consumption, as well as enhanced bag life.
Summary
The successful revamp of the bag house has enabled the customer to enhance the cement plant’s capacity, as the problem of high pressure drop across the bag house has been successfully resolved. On the basis of the customer’s specific conditions, Ecomak Systems studied the problems faced by the client and the engineered the complete project to reduce the pressure drop to within a reasonable limit, as well as reducing the power consumption. The return on investment was found to be more than attractive. The performance of the baghouse is consistent and the baghouse as been in full operation for a period of more than nine months. While giving the performance warranty, it is essential to study and analyse various technical aspects of the baghouse and Ecomak did so successfully. This has been proved at this cement plant.
This article was first published in World Cement magazine in August 2017, titled: Implementing Improvements in India.
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