Earlier this year the Dutch company Duiker Combustion Engineers shared a company paper with Ammonia Energy that targets ammonia energy as an application for the company’s proprietary stoichiometry-controlled oxidation (SCO) technology. The technology’s original commercial deployment in petroleum refining occurred in 2010, and now the company sees potentially broad applications for it as a sustainable energy expedient in the industrial and electricity sectors.
According to its Web site, Duiker is “an engineering company specialized in process combustion solutions.” The company’s “main activities include designing, supplying and installing a range of liquid and gaseous fuel process combustion systems for oil refining, chemical and natural gas processing industries . . .”
The SCO story starts in the 1990s when the European Union initiated regulation of the sulfur content of diesel fuel. Oil companies responded by installing processes that first remove sulfur compounds from crude oil and then convert the sulfur to its readily manageable elemental form. The difficulty of the task is exacerbated by the fact that crude oil often embodies as much nitrogen by weight as sulfur. This means that the initial sulfur removal step (“hydrotreating”) produces as one of its outputs “sour water stripper gas” that consists in thirds of hydrogen sulfide (H2S), ammonia, and water. The commingling of H2S and NH3 creates challenges in the subsequent step of conversion to elemental sulfur in a sulfur recovery unit (SRU). In Duiker’s words, “NH3, if not combusted properly, creates fouling, plugging and corrosion problems in downstream equipment of SRUs.”
The value proposition of Duiker’s SCO technology contains two main elements. First, it involves processing of ammonia in a separate system. Although this system carries a cost, the capital expense per unit of throughput capacity for the SRU can be reduced disproportionately. Second, by sourcing the heat needed for the final tail-gas incineration step in the SRU from the combustion of ammonia, the SRU’s fuel consumption can be reduced or even eliminated.
Of course, improved management of sulfur-based pollutants would not hold much appeal if it created a problematic flow of nitrogen-based pollutants (unburned ammonia and oxides of nitrogen (NOx)). Minimization of these species is at the core of Duiker’s SCO concept. The term “stoichiometric combustion” implies precise control of reactant proportions in the combustion chamber. This is achieved with digitally controlled feed rates of ammonia and combustion air. The SCO module also includes the same optimized, refractory-lined flow paths found in Duiker’s other combustion units; continuous sensing of combustion parameters; and heat transfer characteristics that allow flue gas temperatures to be maintained within a narrow band. The result is complete oxidation of ammonia with flue gas NOx in the range of 50-80 ppmv “@ 3% vol O2 dry” (the technical metric that allows apples-to-apples comparisons of NOx generation and control); and so little unburned ammonia that “we do not detect any remaining ammonia in the SCO flue gases even with highly sensitive NH3 measuring equipment.”
Duiker sold its first SCO unit in 2010 but only a few additional ones in the years since. The company has continued to refine the technology and last year was able to confirm the robust performance of its newest iteration at a customer’s plant in Asia. Then, the company’s Business Development Director, Albert Lanser, decided to attend the 2018 NH3 Event in Rotterdam and while there had an epiphany. “We realized the SCO unit could also be applied in the ‘ammonia to heat’ cycle,” he told Ammonia Energy during a mid-March interview.
As context, Lanser points to emerging policies that seek to limit the future scope of natural gas as an energy staple. While natural gas has generally experienced a vigorous surge in demand over the last decade, a few jurisdictions have started to act on the reality that the commodity is still a fossil fuel, albeit a less CO2-intensive option than oil or coal. The Netherlands is prominent among these jurisdictions. According to a July 2018 article in OilPrice.com (“the most popular energy news site in the world”), “the future of the Dutch gas sector . . . looks bleak due to two important developments in 2018: a political decision to reduce production with a timeline to stop entirely until 2030[;] and a new climate agreement.”
The replacement commodity envisioned by policy makers is electricity. Not surprisingly, natural gas advocates are quick to argue the infeasibility of this proposition. For example, Nareg Terzian, spokesperson for the International Association of Oil & Gas Producers, was quoted in a March 2019 Bloomberg article as follows: “The problem with full electrification [of space heating] is that it sounds great in principle — but it’s very difficult to implement.”
Such sentiments may be overblown, but Lanser points out that full electrification of high-temperature industrial processes really will be a challenge. “Low temperature can be solved indeed with electricity,” he said, “but if you need more than 1,200 degrees C, how are you going to do it with electricity? That’s a real issue.”
Ammonia combustion could be the resolution of the issue, in Lanser’s view — but only if its pollutant emissions can be kept under control. “The combustion properties of ammonia are fundamentally not favorable, but with our dedicated SCO-technology, ammonia combustion is found to be very feasible ” he says, but there is no doubt that burning ammonia can produce large quantities of NOx. This is what the Duiker technology is all about. “Our stoichiometric oxidation allows very limited emission of NOx without the necessity of a deNOx installation,” Lanser says.
High-temperature industrial processes are at the heart of Duiker’s vision for its SCO technology, but they also see potential applications in electricity generation. Lanser says there are two main possibilities in this regard. The first is to burn ammonia to produce thermal energy at industrially relevant temperatures, for example to displace fossil fuels in a steam boiler. The second would be to burn ammonia to heat the compressor discharge air in a gas turbine. This may prove to be a desirable emissions control strategy for an ammonia-fired gas turbine.
Lanser believes that SCO technology provides a flexible combustion platform that Duiker could adapt to a wide range of applications. The next step, he says, is to sit down with a customer and brainstorm ideas: “Is there any application we might think of where we can use our SCO technology to help you overcome the natural gas shortage problem and also the CO2 emission problem?”