Telltale signs from the chimney ANA-DIGI SYSTEMS boiler control cuts operating overheads.

Factories depend greatly on steam generation for most of their production line heating requirements, but these systems tend to contribute substantially to operating overheads.

While traditional boiler control systems are the accepted norm in most factories, inherent inefficiencies in these systems and the need for constant operator interventions frequently result in higher water and coal usage than actually required. Furthermore, the specialised dedicated parts needed to maintain these boiler control systems are typically only available from the original manufacturer.

More efficiency required

According to Keith Gross of ANA-DIGI SYSTEMS, a smoking factory chimney stack is a telltale indication of inefficient combustion and coal wastage. Seeking to provide technology solutions that optimise productivity and reduce overhead costs, ANA-DIGI has recently been involved in the creation of a more efficient boiler control system at a large factory run by one of South Africa’s top fast moving consumer goods companies.

The factory engineer investigated the possibility of automating the main factory boiler in order to improve combustion and reduce the amount of coal and water usage. The proposed new system would use the desired steam pressure set-point as the basis for control, which would ensure that only the amount of coal required to provide this would be consumed.

New automation technology solves the problem

ANA-DIGI was contracted to supply a simplified and more versatile system and implement the required system upgrade. As much of the Western Cape factory already ran on the LS PLCs and VFDs that the company supplies, LS iS5 inverters were chosen to control the ID and FD fan speeds, and an iG5A inverter to control the stoker speed.

Fan speeds are regulated by a combination of feedback from the steam set-point and the setting of the photo-helic pressure differential controller. The stoker conveyor speed is then controlled by way of feedback as an integrated part of the control philosophy.

In order to determine exact coal usage, an IMO i3 PLC carefully monitors the rate of coal feed and reports the usage in tons per hour. The built-in touch screen HMI displays the coal usage values for monitoring purposes. Additionally, this unit has built-in GSM dial-up facilities, which can be used for remote system fault reporting.

The start-up procedure in the main boiler was also simplified. Initially on start-up, because several safety interlock conditions must be met, the boiler system was started in manual. As the boiler pressure built up and the safety interlocks were satisfied, automatic mode was then engaged.

The results speak for themselves

The results of the new system have been encouraging to date. Over-pressure blow-off of steam has been virtually eliminated due to the accuracy of the automation, which has resulted in substantial savings in water consumption and coal usage.

The advantages offered over the old boiler control method have been well received. “The biggest problem to date has been in preventing operators from switching the control back to manual,” says Gross. “Getting them to understand that when the boiler goes into sleep mode they do not need to switch to manual and adjust the coal feed rate has been difficult.”

Following the success of the boiler control system in the Western Cape, four large boilers have been similarly upgraded at the company’s Gauteng facilities.