Boiler technology |


Left: New boiler at the Petronas methyl tert-butyl ether plant, Kuantan, Malaysia. This is designed to burn a high-hydrogen-content fuel stream (source: PETRONAS)


Above: Superheater temperature variation (°C) at fuel switch to hydrogen (as measured at site)


The boiler capacity is 57 t/h superheated steam with a minimum uninterrupted operation period of three years.


The design fuel is natural gas (NG) and offgas with various mix compositions. One mix composition anticipates over 97% hydrogen content, with all the implications that entails, as explained below.


Hydrogen challenges A boiler capable of burning several fuel gas compositions must be designed to handle different densities in fuel valve trains and burners. The control system must be able to manage different heating values of the different fuels as well. High H2 increases thermal NOx


content in fuels also emissions so specially


designed primary and secondary control measures are required.


Among issues to be considered: ● The density of hydrogen is eight times lower


than natural gas, therefore, its specific volume is considerably higher, and all burners, valves and skids must be redesigned accordingly. In order to quantify the impact, we see that for the same thermal power, NG mass flow is 2.326 times H2


mass flow and in terms of volume flow H2 3.533 times normal NG volume flow.


● The H2


flame temperature is higher than the NG flame (NG adiabatic flame temperature 1890°C/3434°F; H2


is


could be the most interesting primary measure. An optimised catalyst reactor could also be needed in some cases.


● On the other hand, H2 flame heat radiation


is lower than for the NG flame, therefore heat exchange by radiation in the furnace is probably lower with H2


adiabatic flame temperature:


2060°C/3740°F). As the heating value is higher than NG, designers must consider higher temperatures of the flue gases and less mass flow. Therefore, the furnace size, the attemperator system, the flue gas distribution and the thermal NOx


relation to NOx


control measures must be reviewed. In control primary measures, the


most common approach is using recirculation. The solution requires careful analysis because an increase in nitrogen could also increase the NOx


. Steam injection to lower the flame temperature than with natural gas.


All these changes in flame temperatures and heat radiation must be also considered during operation. In this kind of multi fuel boiler the control system must fit the boiler operation to adjust transitory temperature peaks when switching the feeding fuel.


● The composition of flue gas from H2 combustion is 24% H2


O, 73% N2 1% Ar, by weight; or 33% H2 , 2% O2 O, 64% N2 , and , 2% O2


and 1% Ar, by volume. So, special care should be taken in dealing with flue gas condensation at the back end of boiler ducts. Thorough analysis of water dew point and/or any internal coating in the exhaust ducts is required.


Petronas perspective


The existing boilers at Kuantan have served us well for over 20 years, but the new and improved boiler strengthens our overall steam supply availability and production reliability. We look forward to utilising the full potential offered by the new equipment, enabling us to adapt towards changes in fuel composition as well as other external challenges. During project execution, Petronas


worked with divisions of Wood in different countries (including Spain as well as Malaysia). Despite geographical differences and interface challenges, the level of co-operation and collaboration on the new boiler project was really good. The various parties were focused on meeting the same objective – to ensure the boiler project could be delivered


safely, on time, and within budget. Local presence played a significant role in ensuring seamless communication within our teams. Occasional physical meetings were effectively utilised to resolve many issues and differences in understanding actual client expectations. In the end, we are proud to be part of the team which collaborated and delivered the project successfully despite various challenges throughout the journey. As to the future role of hydrogen, we


envisage essentially three phases: ● The amount of H2


available today cannot


fully meet industry demand. Burners in existing boilers are adapted to enable


a significant proportion of available H2 to be burned mixed with current fuel streams.


● When the amount of H2 available


is significant enough to meet steam demand, a dual fuel hybrid boiler, allowing H2


● The zero emissions target can be achieved when quantities of H2


and / or NG to be burned


depending on the availability of each, is the best strategy to adopt.


can be


reliably produced in quantities satisfying industry demand. Under this scenario a dedicated hydrogen boiler capable of generating steam to meet industrial requirements, with high efficiency, zero CO2


emissions and very low NOx be the best solution.


M Al-Azahary B A Sani, project manager, group project delivery, Petronas


, would


50 | October 2021 | www.modernpowersystems.com


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