Changshan’s new fan
One cement producer to benefit from a cost-saving energy retrofit is Changshan South Cement, China. Changshan South Cement Co Ltd had equipped its two clinker production lines with MC-2x39No30.5F raw mill circulation fans, manufactured by a local company.
However, the low efficiency of the fans led to the motors being operated for a long time at an overloading current.
Moreover, the actual power of the motor had been far above the rated power, resulting in excessive energy consumption and a potential safety hazard. The challenge for the cement company was to reduce the energy demand of the raw mill fans as much as possible.
Make sure to download the pdf to read the full case study including specifications of fans and testing analysis
Road to improvement
To achieve this goal, Changshan South Cement Co Ltd asked Howden to improve efficiency and lower energy consumption with a retrofit of the circulation fan. Following a full analysis by Howden engineers, the fan supplier proposed to start renovations at the first kiln line to reduce the disruption of daily operations.
To accurately determine the system’s actual requirements in terms of the fan’s air volume flow and pressure, and thus improve the efficiency of the renovated fan together with the existing system, Howden undertook an on-site performance test.
The test results show that the low actual operational power of the fans had led to a considerable waste in energy as well as highlighting that the motors had been operating in an unsafe current range of 230-240A, which is above the rated current.
Based on the on-site test data and considering the system’s situation and the production requirements, the design parameters of the new fans were confirmed. This included a reduction of the air pressure by 250Pa and an increase of the air volume by 60,000m³/h.
Reconstruction
Taking these new design parameters and the need to improve the fan’s power consumption into account, Howden selected its more efficient L-series backward-curved blade fan (Model No L5N 2655.00.08 DBL6T).
The new Howden fan was designed to use significantly less shaft power than the original one, enabling the old motor to be used. Moreover, special composite wear-resistant liners were used on the blades of the new Howden impeller, making them more abrasion resistant while increasing the efficiency of the fans.
The replaced components included rotor, housing, inlet cones, bearings and bearing housings, couplings and dampers. Components that were kept intact included the concrete foundation, anchor bolts, motor and actuators. In addition, the retrofitted fan has made full use of the original civil foundation. The main body of the foundation has been kept intact with only some partial reconstruction to shorten the installation time of the new fan.
Howden has also undertaken extensive on-site surveying and mapping to match the reconstruction work with the original cement foundation and reduce the ducting alteration as much as possible.
New fan performance and economic analysis
The new fan was installed when the cement plant was overhauled. The old fan was removed and the new one tested for a trial run – all in the short time available. The comparison between the test value and the design value showed that the actual operating point was close to the original design point, indicating that the original goals of the fans’ actual operation efficiency were fully achieved.
The test data show that the flow and total pressure of the fan have been improved and the fan efficiency has been greatly enhanced after the reconstruction. The motor power dropped from 3765kW to 2994kW and the current value range fell from 230A~240A to 170A~180A, indicating a significant saving of energy. This data shows that power consumption has been lowered by 771kW/h (3765kW-2994kW) while material output following the retrofit has remained the same. On the basis that fans are operational for 700h annually, this saves 771kW x 7000h =5,397,000kWh of electricity.
At a cost of CNY0.55/kW, this amounts to savings of CNY 2, 968, 350 (US$ 431,332) per year. This cost analysis shows that Changshan South Cement Co Ltd was able to benefit from an extremely short payback for this retrofit project.
Changshan South Cement Co Ltd also carried out a comparison between power consumption during the 72h before and after the fan reconstruction. This showed that the average power consumption of the raw mill process has been reduced by 2kW/t under the same raw material output after the circulation fan retrofit.
Feedback
Changshan South Cement Co Ltd was very satisfied with the performance of the new Howden fan and has carried out several new cement fan retrofits with Howden since. The Chinese cement producer awarded Howden with a technology innovation award for the reconstruction.