ABB drives increase productivity for Biomass plant
Installing ABB drives and controls at a problematic biomass steam generating plan in Brazil has resulted in improved productivity, higher sales and lower energy costs. The Brazil plant produces saturated steam in two low pressure boilers. However, the outdated controls were inefficient and prone to frequent disruption and downtime, resulting in lost revenue. The use of equipment from many different vendors was a factor in the process instability.
Biomass fuel (wood chips) discharges into a channel before being transferred by a screw and conveyor system to a rotary dryer. After drying, the chips are fed into furnaces to heat the water in the boilers to 160 to 180 °C. Fans maintain a balanced air flow into and out of the furnaces to ensure the correct combustion rate. Furnace temperature is maintained at 600 to 700 °C. Steam is produced at a rate of 35 t/h and a pressure of 14 kg/cm2.
EXTENDED AUTOMATION & SAFETY
The process was upgraded to automate as many production stages as possible. The goal was to minimise operator intervention and improving safety by incorporating interlocks into the process. They installed a total of thirty-five 110 kW ABB drives, together with HMIs, PLCs, and associated equipment.
The project also included installation of interactive, user-friendly control screens that deliver a large amount of information to the operators in an easy-to-understand format. Following the upgrade, field sensors monitor the production process and feed data to the ABB PLCs, which send command signals to the drives to control the process equipment.
Processes upgraded included the:
– fuel handling screw and conveyors, and the dryer metering valve
– furnace FD (forced draft) and ID (induced draft) fans.
– integration of fan control and fuel feed
– the treatment system demineralises the water before pumping it to the boilers
– boiler feed water pumps
– electrostatic precipitators used to treat the furnace exhaust gases
– flow rate and pressure of the output steam
ABB drives increase productivity
Following completion of the upgrade, the process has been stable and reliable. It now generates steam at a consistent pressure and flow rate. Maintenance costs and downtime have both decreased. In addition, as a result from the improveed performce, the company was able to streamline its headcount.
The use of drives means less stress on the electric motors, which had previously been subject to high-temperature damage. Consequently, the project reduced the current required from the network so it was not necessary to upgrade the transformers or power cables. As each motor is now supplied via its own drive, the system is very flexible: the speed of a specific shaft can be changed without having to change pulleys, for example.
Benefits and payback
According to the plant operator, the improved production without interruptions has led to a £65k per month increase in sales revenues and a reduction in maintenance costs of around 20%. In addition, cost savings of £50k per month through reductions in electricity consumption, employee numbers and downtime gave the project an eleven-month payback period.
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