Hanson Brick fires up energy savings

Tamworth, UK - Hanson Brick  has knocked £60,000 off its energy bills following an an energy audit to investigate the usage of the many fans in operation within the kiln processing at its Tamworth plant.

The audit, conducted by PPT Drive Systems, revealed substantial energy consumption through a number of powerful fans used in the brick firing process. In total, 14 fans were identified as potentially benefiting from the control offered by variable speed drives.

The fans in question all ran 24/7/365 which equates to 8,760 hours each every year. Ratings included five motors at 11kW – four on the preheat oven and one on the main kiln contravent – and another at 4kW on the contravent.

The two main kiln burner fans were rated at 30kW, while the main kiln rapid cooling and control cooling fans were both 22kW. A 30kW main kiln recoup fan; two 7.5kW fans cooling under the cars; and a main kiln final cooling fan of 22kW completed the installation.

PPT’s engineers estimated that all but one of these fans could be reduced in speed from between 10% and 20%, with the remaining single fan reduced by 5%. Previously, eight of the fans had damper controls fitted – the remainder had no controls at all. Although dampers are often used to regulate the output of fans, reducing the speed of the fan is a much more energy efficient way of achieving the same effect.

With damper control, the input power reduces as the flow rate decreases. However, under VSD control, the variable torque characteristic of the fan means that the relationship between flow and the speed of the fan is such that the input power reduces in a cube law relationship with the speed reduction. The energy expended using a VSD is significantly less than that of damper-controlled motors.

Hanson Brick opted to install Altivar VSDs from Telemecanique, a brand of Schneider Electric, in IP20 ratings since they were ultimately to be housed in IP66 rated enclosures from  Schneider company Sarel. The housings also featured Telemecanique door interlocked switch disconnects suitable for use in dusty environments. Because of the harsh environment of the brickworks, the VSD’s keypads/graphical display units were housed behind an IP65 rated opening window.

The VSDs were located near to existing starters within a suitable unistrut framework. The mains feed to the existing star-delta starter contactor arrangement was disconnected and new cabling was connected to the VSDs’ main inputs. Main cabling from the star-delta starter was replaced with new cabling from the VSDs to the existing motor terminals.

Existing motor cabling was permanently arranged in three parallel pairs with the motor windings in permanent delta connected configuration. The VSD ‘run’ signal was connected across one pole of the existing star-delta starter contactor ensuring that an existing PLC control was unaffected. The VSD speed references are selected manually via the drives’ keypads.

While the original calculations for energy savings predicted a pay back within 12 months, these estimated figures relied on making assumptions about consumption, electricity units costs and so forth. In practice, once the new motor controls were in place, the savings were significantly higher than predicted.

Without the VSD controls, the total absorbed power was 204kW with a total annual consumption of 1,787,176kWh and an energy cost of £107,231.00. This equates to 768 tonnes of carbon emission per annum. Under VSD control, the same kiln system absorbs just 90.5kW with an annual consumption of 792,780kW and an energy bill of £47,567.00 a year and an amortisation of the capital investment in eight months.