Control of Industrial and Commercial Boilers

Control of Industrial and Commercial Boilers
Based on many years of successful boiler control using the very successful AC Station®,
Ascon is now enhancing the future of boiler control with an entirely new and innovative
control product called SigmaPAC®.
Today, the efforts of boiler manufacturers are focused on research and development of
processes that are able to meet stringent local and international standards for energy
saving and pollution reduction. These solutions range from the use of low NOx burners to
complete burner control systems that are able to integrate all aspects of control. The build
up of nitrogen oxides is in large part due to the high temperature which the burners operate
and to the length of time the combustion by-products are in the combustion chamber. One
of the latest developments is the use of high efficiency condensing boilers.
These boilers incorporate an extra heat exchanger where the hot exhaust gases are used to
pre-heat the feed-water. The water vapor, which is present in the flue gas, condenses and
the latent heat is recuperated. The development of modern boilers needs to be
accompanied with the use of the latest state-of-the-art control and monitoring systems.
Automation equipment is now able to offer distributed advanced control solutions with
practically unlimited connectivity, enterprise data integration capabilities and a high level of
flexibility. All these characteristics are now available in the “Programmable Automation
Controllers” also called “PACs”.
What is a SigmaPAC®
To satisfy the increased requirements for process control applications, Ascon has
developed a control system that is able to incorporate the benefits of programmable logic
controllers (PLC) with those of process controls and PC-based systems. Most boiler
systems require combined control functions of both discrete controllers and digital inputs
and outputs of a PLC. For example, a complex algorithm for PID control of pressure or
temperature requires additional hardware and software programming. Device
interoperability, data integration, and network connectivity also require additional
processors, gateways and software integration. A PAC includes all the above-mentioned
features in its design, and is generally modular in design and construction, allowing for easy
expandability. The same type of equipment can be used for small commercial boilers, as
well as large industrial boilers. Ascon’s SigmaPAC® system has been developed using the
experience gained in the manufacture of both control instrumentation and automation
components since 1969. Where it goes beyond the standard PLC is in the area of
computing: the SigmaPAC® can execute complex algorithms, advanced PID, floating point
operations, and run dedicated analog measurement and control functions. The multi
function platform of SigmaPAC is equipped with control strategies for many types of control
variables (temperature, pressure, flow, level, position…), logic and sequence functions, and
process calculations. The SigmaPAC® connects directly to the SigmaPAC® I/O modules
through a high speed CANbus protocol using standard RJ45 connections, and it also comes
standard with two Modbus master/slave serial ports and one Ethernet port.. The application
programming is performed using IEC 61131-3 compliant software called OpenPCS.
Since each variable in the boiler process influences all others, boiler manufacturers know
the process is one of the more critical and difficult ones to be controlled. Also, industrial
boilers are subject to frequent and quick load changes. These systems typically include
outlet main header steam pressure or water temperature control (master), combustion
control with air/fuel ratio and trim adjustment, three elements drum level control, combustion
chamber draft control, burner management and interlocks. It may also include load
distribution control if more than one boiler is connected to the same header. A number of
variables and status conditions must be measured, detected, displayed and controlled in a
fast and reliable way. This is all accomplished with the new SigmaPAC® and OP touch
panels from Ascon. The SigmaPAC® I/O modules handle measurement linearization, data
scaling, engineering units conversion and alarm handling. This allows the SigmaPAC®
processor to focus on more important process functions such as master control with
linkage-less parallel positioning, the PID algorithms, cross-limiting for the combustion, boiler
efficiency and fuel gas mass flow computations and lead-lag sequencing. The controls of
the boiler can be managed from an operator panel connected to the SigmaPAC® system.
Such panels permit an easy and effective means to visualize the entire boiler process.
For more information, contact Ascon Corporation at www.asconcorp.com of phone 630-482-2950.