April 2021

32 | Plant & Works Engineering www.pwemag.co.uk April 2021 Energy & Environmental Management Focus on: Boilers, Burners & Controls boiler size) on three steam boilers that generate superheated steam. However, they would be equally suitable for hot water boilers or thermal oil heaters. According to Krausnick, the specific requirements at Nouryon also led SAACKE to develop a standard H2 version of the SKVGD for a wide range of applications. The scope of delivery also included the SAACKE burner and boiler control system se@vis pro as well as a flue gas recirculation system with separate fan. Exhaust gas recirculation Despite all its potential, the thermal use of H2 requires some technological measures. Compared to natural gas, hydrogen produces three times as much NOx emissions, due to its higher adiabatic combustion temperature and approximately eight times higher flame speed. Krausnick says SAACKE countered this problem with a sophisticated external exhaust gas recirculation system. This process ensures dilution effects and cooling of the flame by mixing inert exhaust gases into the combustion air. In this way, the emissions in Ibbenbüren in hydrogen operation can be brought into line with those of natural gas (see Table 1). This means that the plant not only complies with the current legislation on emissions, but even falls significantly below these limits. This is because, depending on the intensity of recirculation, emissions drop further to about 40 mg/m3 @ 3% vol. O2 in the dry flue gas (see diagram 1) , even though a relatively high recirculation ratio is currently still necessary for this. NOx emissions as a function of the maximum recirculation ratio (RV) of the exhaust gas at Nouryon in Ibbenbüren (Source: SAACKE GmbH) Furthermore, the high H2 flame temperature also places special demands on the material. SAACKE responded to this with heat-resistant steel and a special gas injection design. In addition, Krausnick explains that SAACKE experts have the pipe for the hydrogen feed flushed with nitrogen before the burner ignition in order to increase the safety aspect. Automated control Since the SKVGD burners can be operated variably with up to 100% pure hydrogen, completely with natural gas or in any mixing ratio and are also designed for operation with light oil as an emergency fuel, a special challenge arises: The performance-specific demand for supplied air as an oxidant differs significantly. Therefore, the SAACKE control system regulates the air volume depending on the fuel mix. The extremely low gas pressure of hydrogen (50 mbar(g) before entering the gas control line) requires the use of a special gas line with a particularly low pressure loss. For this purpose, a dynamic pressure probe was installed to measure the volume flow and soft- sealing flaps were installed as valves, instead of using commercially available turbine meters and quick-acting valves. The project example shows that the large- scale thermal use of hydrogen, with industrial burners, is possible and available now. Stephan Richter, head of technical service at Nouryon emphasised: “The hydrogen burners make an important contribution to reducing the CO2 footprint of our processes. SAACKE provided us with optimal support and advice on all questions and challenges relating to the project.“ 0 7 : C X:,4$ c,-(4$4131&$$ J?A1,0,=$3,(8:',=$0(4:,$ L(&:'(4$-(8$ WWN$3-d3Q$ WNN$3-d3Q$ <.='2-,+$ >NN$3-d3Q$ WNN$3-d3Q$ c1-A&$214$ >NN$3-d3Q$ >NN$3-d3Q$ Table 1: Limit values for NOx emissions at Nouryon in Ibbenbüren (Source: SAACKE GmbH) Diagram 1 The bluish-transparent H2 flame of a SAACKE combustion system - for the human eye, these shimmering flames are often difficult to see. NOx emissions as a function of the maximum recirculation ratio (RV) of the exhaust gas at Nouryon in Ibbenbüren (Source: SAACKE GmbH)