Boiler and Burner Control System Upgrade

Overview

A chemical processing plant in the Vaal Triangle operated two 10-ton steam boilers with burner management systems based on obsolete relay logic and a Siemens S5-115U PLC. The system could no longer meet updated safety standards, spare parts were unavailable, and insurance auditors had flagged the burner control system as a critical non-compliance risk.

The Challenge

The existing burner management system used relay-based flame safeguard logic with a Siemens S5-115U PLC for sequencing. The S5 platform was obsolete — Siemens had discontinued support, and replacement modules could only be sourced from the secondary market at exorbitant prices. The relay system lacked self-diagnostics, making fault finding time-consuming. More critically, the system did not meet NFPA 85 requirements for burner safety, and the plant's insurance auditor had given a 12-month deadline to achieve compliance. Flame scanner response times and purge cycle timing could not be reliably verified with the existing hardware.

The Solution

Cretek engineered a complete burner management system replacement using a Siemens S7-1500F fail-safe PLC (F-CPU) with TIA Portal F-FBD safety programming. The system included dual flame scanners, safety-rated burner sequencing, purge cycle verification, fuel-air ratio control with cross-limiting, and a new WinCC Unified HMI. A hardwired safety shutdown chain was implemented per NFPA 85 requirements. The system was fully tested through FAT and SAT with witnessed testing by the insurance auditor. Commissioning was completed during a planned annual shutdown to avoid production impact.

Results

• Full NFPA 85 compliance achieved, satisfying insurance audit requirements and reducing premiums
• Burner efficiency improved by 12% through precision fuel-air ratio control and oxygen trim
• SIL 2 safety certification achieved with documented safety lifecycle per IEC 61511
• Modern diagnostics reducing fault-finding time from hours to minutes via the HMI
• Seamless migration executed within scheduled annual shutdown — zero production days lost

Technologies Used