Current Topics in the North American RICE Industry

By Christopher Marks, PE, Burns & McDonnell

In recent years, Reciprocating Internal Combustion Engines (RICEs) have been utilized in the North American market to generate electric power and provide fast response to load fluctuations. As such, they have had an important role in maintaining a stable electrical grid. While the majority of these units have operated solely on natural gas, some areas have also utilized liquid fuel in order to provide stability where firm gas supply is unavailable or uneconomical. As the market continues to develop, new technologies have emerged that may impact the utilization of RICEs in the near future.

Primarily, large RICEs (7-20 megawatts [MW]) installed in North America have been of the four-stroke lean-burn variety. These engines have operated with good efficiency, high reliability, and impressive startup and ramp times in order to provide peaking power to the grid. However, RICEs are also used extensively in marine applications to power cruise ships and large freighters. In these applications, two-stroke RICEs operating on liquid fuels have also proven themselves as reliable and efficient prime movers. Their high power-to-weight ratio enables more cargo to be loaded without sacrificing power. Additionally, there are several land-based installations utilizing similar RICEs throughout the world. In general, two-stroke engines can achieve the same emission limits as four-stroke RICEs, though additional controls are required. Also, the two-stroke units are more reliable and efficient when operated continuously. Two-stroke RICEs are able to achieve efficiencies over 50%, while their four-stroke cousins are typically limited to less than 46% efficiency. It should be noted, however, that two-stroke engines require the lubricating medium for the cylinders to be a part of the fuel mixture. This makes them incapable of operating solely on natural gas, as is common for four-stroke RICEs in North America. They require at least 1% of their fuel supply to be liquid fuel in order to ensure that proper lubrication is maintained. Furthermore, the two-stroke engines offer more fuel flexibility than four-stroke engines and can efficiently operate on low-grade sources of liquid fuel.

However, the features that make two-stroke units advantageous are not significant impacts in the North American power generation market. In this arena, RICEs are typically operated in peaking and spinning-reserve modes, which negates the improved reliability of the two-stroke RICEs. When used in peaking applications, there is no conclusive evidence that they are more reliable. Furthermore, while the increased efficiency appears to be advantageous, this is offset by the additional costs required to install a liquid fuel system and provide additional emission controls to meet the strict permitting requirements of the market. Finally, the two-stroke RICEs’ ability to operate efficiently on low-grade fuels loses significance when high-quality and consistent fuels are readily available. It is for these reason that several manufacturers have chosen not to offer their large two-stroke RICEs in the North American market, though there does seem to be demand for smaller units (3-7 MW) that can run as base-load and avoid triggering Prevention of Significant Deterioration (PSD) regulations. Thus, they could be well suited for co-generation or other facility-focused power generation applications.

Another topic in the current market is battery storage. Large-scale battery “farms” are increasingly being viewed as an economical way to reduce volatility on the electrical grid by stabilizing demand and allowing renewable generation to appear more like base load. The theory is that batteries will charge from the grid when generated power exceeds demand and then discharge that power when demand outstrips supply. Until recently, lead-acid batteries had been the most economical option, but their short lifespan of 3-4 years prevented their widespread adoption. Recent advances in Lithium-Ion batteries, with their large capacities and long lifespans, have raised expectations that battery storage will become more profitable.

The question in regard to RICEs, then, is how do they co-exist in a market where batteries are able to reduce and replace the need for their ability to stabilize the grid? On a macro-scale, they do seem to be redundant technologies. However, it is in smaller-scale applications where the two are able to effectively co-exist. Many municipalities and other small-scale power providers already view RICEs as an effective means to free themselves from the fluctuations of market pricing and Power Purchase Agreements (PPAs). When electricity prices are low, it is economical to purchase power to charge batteries and store it for when prices begin to rise. When power pricing is higher, the RICEs can be used to offset the cost once the batteries have been depleted.

As technology continues to advance, so too do the solutions to market problems. Nonetheless, four-stroke RICEs are still appropriate for the North American market for the foreseeable future, though they can expect to share their role with increased battery storage as that technology continues to mature.