By Teresa Hansen, Associate Editor
High boiler efficiency is vital to power generators trying to trim costs and improve performance with efficient and effective fuel use. Because a boiler’s efficiency is determined largely by the cleanliness of its heating transfer surfaces, many power companies are modernizing their boiler cleaning systems.
An original equipment manufacturer of advanced boiler cleaning systems, Atlanta-based Clyde Bergemann, offers boiler on-load cleaning solutions for most boilers, from individual sootblowers to intelligent boiler cleaning systems.
Intelligent boiler cleaning systems include sensors that monitor boiler cleanliness and provide information that enables the boiler’s control system to decide which sootblower will clean next and where it will clean. This intelligent system improves boiler efficiency and minimizes downtime.
When searching for motor management solutions for the boiler cleaning equipment, Jim Noland, Clyde Bergemann’s controls engineer, looked for a distributed I/O (input/output) solution that would not require individual hardwiring and conduit running to the sootblowers and where basic sootblower operation could be implemented with a local controller. Noland searched for a solution where a single cable could run from a programmable logic controller (PLC) cabinet and daisy chain to the other sootblowers. He also wanted a solution that could operate independently if PLC controls were disrupted.
“We were interested in a solution that replaced hardwired circuitry. Instead of custom circuits for every blower type, we wanted to replace all that wiring with one motor management tool,” Noland said. Clyde Bergmann selected Siemens’ SIMOCODE pro controllers.
“Instead of maintaining separate circuit designs for each blower type, we now just program a configuration in the system,” said Noland. “For each of the different blowers, there is a different control scheme.” For example, a blower may be programmed to insert, pause for eight-tenths of a second and retract. Instead of hardwiring that logic, it can be programmed. This means logic changes are much quicker than when hardwiring was required.
The system also connects well with Profibus and has a simple interface, said Noland. SIMOCODE pro’s ability to interface with Profibus along with its high degree of detail about the blowers’ performance were key in Clyde Bergemann’s decision to use it.
“You can monitor a lot more detail on the motor status than you can on a conventional control system,” said Sandeep Shah, Clyde Bergemann’s technology director. For example, if the current starts to climb too high, the customer can perform proactive preventive maintenance before the blower shuts down.
As with any industrial operating machine, reliability is vital. Systems need to be fail-safe. When a soot blower fails, a part of the boiler cannot be cleaned and combustion residues are deposited on both the heating surfaces and the heat exchangers. This can inhibit heat transfer and reduce the boiler’s efficiency. To ensure the boiler remains efficient and the soot deposits are continuously removed, a reliable system is vital.
Though Clyde Bergemann engineers knew they wanted a distributed I/O solution, they also knew they could not depend completely on the PLC for safety precautions.
“The first question that always arises when distributed I/O interfaces are considered is: what happens if the communication cable connection is disrupted?,” said Shah. “The fact that the SIMOCODE pro will execute its own logic internally really caught my attention.” The Siemens solution allows for local programming and control, meaning operators can work manually from the sootblower junction box if the Profibus cable is cut or disturbed, or if the controller and device aren’t communicating.
The Siemens system also has the ability to detect limit switch problems, allowing Clyde Bergemann to actively monitor its soot blowers instead of reacting when one stops due to a failed limit switch. “Previously, if a limit switch failed, we would not know until the blower had started and its cycle time was exceeded. Now we can monitor blower I/O status and automatically disable a blower if a problem exists,” Noland said.
One benefit that became apparent after the system was installed was its built-in integrated motor safety protection. This provides instant disabling of the starter outputs if an overload or fault condition is detected as well as reversing and other integrated protection. The advantage is that protection logic does not have to be handled by the PLC. I/O points are not consumed with monitoring individual overloads. Overload trips can be reset from the human machine interface. Overload warning and trip configuration allow different programs to be configured based on the overload’s severity.
For example, in a typical overload condition, the blower should immediately retract and not trip to prevent boiler damage. For a stalled rotor condition, however, the starter should not trip to prevent drive train damage. This level of configuration isn’t possible with a standard control system. It would require additional programming or hardwiring.