St Marys Cement’s Charlevoix Plant is located in Michigan, and is owned by parent company Votorantim Cimentos. The plant has been in operation since 1967 and is a leading supplier of cement throughout the Great Lakes.
The original pre-heater tower was installed in 1978 and was equipped with a fan from the Green Fan Co. (now part of Howden) and was retrofitted in 2002. Performance studies by the customer in 2020 identified that although there were no technical issues, the fan was not performing at optimal efficiency and there was an opportunity to save power and increase capacity.
The Challenge
The aim was to retrofit the existing Kiln Induced Draft (ID) Fan and achieve energy savings with a future 10% capacity increase. Key considerations were time, budget and the need to switch to anti-friction bearings since the existing fan was fitted with a bearing sleeve with a recirculating oil bath and heating system.
The Solution
Howden completed several studies and created a proposal to retrofit the fan, which was agreed to by St Marys. Before proceeding with the project, Howden recommended a field performance test to ensure that the data obtained from the Distributed Control System (DCS) was accurate. U..S company, Air Flow Science, conducted field-performance testing of the Kiln ID Fan in July 2020.
Based on the test results and subsequent discussions between Howden and St Marys process engineers, the new duties for the retrofit were defined.
During field testing, the kiln load capacity was 5,500 tpd and the corrected figures were calculated based on the following considerations:
- Maximum mass flow of 310,327 kg/h, which, added to the water injection, becomes a flow of 497,371 cu. meters/h.
- The required 10% increase in production, which according to the fan laws results in a 10% increase in flow and 22% increase in pressure.
- All corrections were made based on the kiln capacity.
Based on these considerations, the operating points were defined as follows:
Using e-Technopal Software Technology, the data defined in Table 1 and considering the reuse of the existing Green Fan housing, Howden’s proposal was based on the figures in Table 2 (right). Howden selection software identified the best wheel to fit the existing casing to avoid any losses and maintain the best possible efficiency.
Using e-Technopal software and proven experience and knowledge, Howden’s application engineering team identified the need to adapt the cutting area to avoid extra losses and noise. A cut-off modification was also supplied and installed by the customer.
The Outcome
The Retrofit Rotor set was installed in March 2021, and after one month of operation with the kiln maximum capacity reached, the actual savings exceeded the expected savings.
The energy savings of 371 kWh translates to cost savings of approximately $200,000 per year. Based on this data, the customer’s return on investment (ROI) will be less than three years.
In addition to the energy and cost savings, the Howden solution resulted in other benefits for the customer:
- With the new Variable Frequency Drive (VFD) installed, the customer can control the fan flow via speed control. This will maintain almost the same efficiency for all tasks, resulting in savings throughout the process, even with the increased capacity.
- Response time was critical to the success of the project, and Howden specialists in South America were able to reduce the lead time and allow the customer to install the fan as scheduled during the winter outage.
- The wheel was supplied with specially welded chrome carbide wear plates to ensure protection against abrasion and to minimize build-up on the back of the blades.
- Howden provided a technical consultant to be on site and supervise the installation, helping the customer to make mechanical adjustments and ensure alignment. Combining Howden expertise and the customer’s experience, the fan is operating in a low vibration range with low bearing temperature.
- Based on the new performance, the customer can switch from a 4,000-hp motor, to a smaller 2,500-hp motor, including VFD, to ensure full motor shaft load and best efficiency.
Votorantim Cimentos North America and St Marys Cement are extremely satisfied with the performance of the retrofitted fan, and the energy and cost savings have exceeded expectations.
Howden – Kiln Inducted Draft (ID) Fan: www.howden.com
