Decarbonisation Technology – August 2021

Strategies for decarbonising combustion processes Operators can leverage the combustion reaction to decarbonise fired equipment, optimise energy efficiency, enhance process reliability, and reduce emissions

Tim Tallon AMETEK Process Instruments

A midst the global movement towards renewable energy sources, combustion remains an important heating source across many industries, including power and steam generation, oil and gas. While many of these combustion processes continue to operate on fossil fuels, we can derive ‘greener’ forms of combustion by considering the available ‘levers’ inherent to the combustion reaction. With an intuitive working knowledge of these levers, we can more clearly reveal opportunities to meet short-term sustainability targets and long-term strategic roadmaps. First, consider the primary elements of combustion: fuel, oxygen and heat. At sufficient air levels, the fuel combusts with the oxygen largely to produce carbon dioxide (CO 2 ) and water (H 2 O) with trace part-per-million (ppm) amounts of combustibles (which includes carbon monoxide [CO] and hydrogen [H 2 ]) and nitrogen oxides (NOx) both as a result of imperfect mixing and localised flame hot spots. The standard combustion reaction (using natural gas) can be summarised in Equation 1 or generalised (using a generic CxHy hydrocarbon) in Equation 2, as shown below: CH 4 + 2 * O 2 + N 2 → CO 2 + 2 * H 2 O + N 2 + ppm CO + ppm H 2 + ppm NOx eq. (1) CxHy + (x+y/2) * O 2 + N 2 → x * CO 2 + y * H 2 O + N 2 + ppm CO + ppm H 2 + ppm NOx eq. (2) While it may seem simple for strategic discussions, the combustion chemical reaction provides an insightful framework for identifying the various levers available to decarbonise combustion. Notably, each reactant component plays a direct

CO 2HO

ppm CO ppm H ppm NOx N

2O + + N

Figure 1 The combustion chemical reaction, highlighting the key levers for decarbonisation

role in the heat generated and consumed during the combustion process. For example, increasing fuel consumption directly increases CO 2 emissions. In the same way, decreasing the fuel directly reduces the amount of CO 2 generated. From this lens, there are four critical levers that each offer a pathway to decarbonise combustion (see Figure 1 ):

➊ Fuel ➋ Oxygen

➌ Available heat ➍ Carbon dioxide

The following sections highlight the importance of each lever and how specific adjustments to these levers work together to reduce CO 2 emissions. Energy efficiency The first approach to decarbonising fired equipment is to make these assets more efficient. Through increased energy efficiency, the system produces equal or better performance while also consuming less fuel. There are two common approaches to decarbonise fired equipment via