06/04/2022
Controlling Thermal Oxidizer and eliminating of toxic and explosive emissions
During formalin production gaseous by-products are produced in addition to the desired main product formaldehyde. This gaseous by-product stream is an explosive mixture consisting mainly of hydrogen and nitrogen in addition to traces of organic compounds.
HEXION relied on HIMA‘s expertise to modernize its thermal oxidizer system in Duisburg and to implement a high level of safety: A SIL 3 controller of the HIMatrix family and a BCS/ BMS application (boiler protection and control inclusive burner management system) ensure residue combustion including steam generation with a heat recovery steam generator HRSG that is installed in the flue gas system. Thermal oxidizer represents an optimal solution for eliminating the pollutants contained in the gaseous by-product, while enabling an energetic use of the produced waste gases in a HRSG.
HIMA implemented this extremely challenging technology in a two-year engineering period starting from the concept phase through the HAZOP, SRS, system design and programming phases to the commissioning and optimization phase. The project included the rebuild of instrumentation, safety and process technology. Following a hazard and risk analysis, it was possible to achieve a higher and improved safety level. After recommissioning in early 2021, HEXION benefits from optimized, safe and standard-compliant operation of the critical plant in accordance with the state of the art.
Stabilized Process Values in Thermal Oxidizer and HRSG
In the thermal oxidizer, an off-gas burner converts up to 8500 m³/h of gaseous by-product. Gaseous by-product from the upstream production plant is burned completely using a high-temperature combustion at approx. 900°C. This is an important aspect regarding the reduction of pollutant emissions. The decisive factor here is the ratio control and monitoring of the gaseous by-product and combustion air. The BCS/BMS application ensures that the process values are kept stable. The control system intervenes and corrects deviating process values immediately after occurrence. If safety-relevant limits are exceeded, the control system will shut down the plant accordingly, and therefore also increasing plant availability. Further, the process values are kept stable in the HRSG before the safety control system has to shut down the plant. According to the SIL2/3 requirements in the HAZOP, HIMA built a gaseous by-product / combustion air ratio control structure and a redundant independent gaseous by-product / combustion air ratio monitoring and shutdown interlock.
In addition to the flow rate of the gaseous by-product, its pressure, which is influenced by the production quantities of the upstream located formalin plant, is used as a further setpoint for the combined flow control of gaseous by-product and combustion air. Thus HEXION achieved an environmentally sound operation of the formalin plant in compliance with the requirements of current safety and process engineering standards.
Technical Details
A programmable SIL 3 controller of the HIMatrix family ensures compliance with the safety requirements for the plant.
In addition, 19 safety functions (SIL 2/3), 14 PID controllers, 4 controller cascades and 5 safety-relevant sequences were implemented.
HIMA‘s BCS/BMS firing technology application is used to a significant extent:
- Monitoring of the supply media
- Monitoring of the safety-critical variables (O2, CO, temperature) in gaseous by-product as well as flue gas flow
- Combustion air pressure and combustion air flow monitoring
- Gaseous by-product pressure and quantity monitoring
- Level control and pressure control in the HRSG – three-component control, feedforward control by inlet and outlet balancing (PID controller)
- Maximum pressure monitoring and shutdown in the HRSG
HIMA's Functional Safety teams related to Consulting, Solutions and Services actively supported the modernization project in all project stages up to the commissioning and optimization phase.
Project Support by HIMA in All Phases
The HIMA application team was involved in the project from the concept phase through the HAZOP, SRS, system design and programming phases to the commissioning and optimization phase. In the hazard and risk analysis (HAZOP) phase, HIMA acted as HAZOP leader and contributed its knowledge and firing expertise as subject matter expert. HIMA also took the lead role in defining the protection function and safety levels and prepared the Safety Requirements Specification (SRS). Other tasks of the application team included the design and programming of the safety control system, the factory acceptance test (FAT) and support during commissioning.
Both the TÜV approval process and the TÜV acceptance were supported by HIMA during the later stages of the project. Process optimization of the modernized thermal oxidizer plant then took place during ongoing operation.
“HIMA actively supported or proactively managed all stages of the project up to the commissioning and optimization phase, for example, as HAZOP leader. The burner and boiler safety and control system used, with the programmable SIL 3 controller of the HIMatrix family, makes a decisive contribution to the continuous, safe and standard-compliant operation of the thermal oxidizer and HRSG plant. The rebuilt plant meets the requirements and we were able to significantly increase plant availability and gaseous by-product throughput by optimizing and stabilizing the process values.”
Why you should choose HIMA:
- Experienced safety specialists with expert know-how in process and safety technology
- Excellent support thanks to a flexible team close to the customer
- Highest level of safety and compliance with standards (SIL 3)
- Flexible system expansion with certified function blocks - Easy programming with SILworX
- Secure networking via SafeEthernet
Benefits
- Increase of the plant availability and control optimization. HEXION benefits from a control system that reliably intervenes before a safety-relevant shutdown becomes necessary.
- Implementation of safety-related project management (Safety Lifecycle Services): The HIMA application team provided support in all project phases and carried out the safety-related assessment, for example, as HAZOP leader, as well as the safety-related project management.
- Stable combustion conditions in the combustion chamber: The gaseous by-product / combustion air control system ensures stable combustion conditions in the combustion chamber over the entire load range. This also operates proper at fluctuations in the supply pressure.
- Optimization of gaseous by-product combustion: Through a more precise knowledge and monitoring of the process parameters, it was possible to optimize combustion, which also resulted in energy savings.
- Implementation of the high safety level SIL 2/3: As part of the project, HIMA set up two diverse gaseous by-product / air ratio monitoring systems, which enabled a high safety level of SIL 2/3 to be achieved. The monitoring functions used by HIMA are based on both flow measurements and on pressure curve corrected evaluation of the control damper positions.
- Gaseous by-product and combustion air control and monitoring is based on flow measurements: In a combined control concept, the flow rates of the gaseous by-product and of the combustion air were controlled as a function of each other (cross-feedback). This ensured the optimum gaseous by-product / combustion air ratio in all load ranges.