Dwindling local reserves of natural gas means that more gas must be imported, either by pipeline or by ship as LNG, to meet demand. Since this supply of gas comes from different reserves around the world and is intended for a variety of markets, its composition can vary considerably, and thus imported natural gases generally have a different composition than the gases traditionally distributed. At the same time, the drive towards a ‘greener’ natural gas infrastructure by introducing renewable gases into the gas grid has resulted in the steady increase in the injection of gaseous fuels from biomass into the grid, with other renewable gases being planned (e.g. H2 and syngas). Different compositions can have different combustion properties, which can lead to unacceptable changes in the safety or fitness-for-purpose of end-use equipment. For the optimum and safe operation of gas engines, it is of great importance to characterize the knock resistance of the gases accurately.
Now available: The PKI Methane Number Calculator for Pipeline Gas
To determine the fitness for purpose of pipeline gas, DNV GL has developed a generic, next-generation method to quantify the knock resistance of pipeline gases based on the combustion properties of the fuel.
Similar to the existing DNV GL PKI Methane Number Calculator for LNG, the pipeline gas calculator computes a PKI methane number to quantify the so-called knock resistance of the fuel on a 0-100 scale analogous to the octane number for gasoline. The calculator allows computation of compositions typically found in pipeline gas and pipeline gases mixed with renewable gases, such as H2, CO, CO2 and substantial fractions of N2. The predictions of knock resistance for a wide range of fuel compositions has been verified for a lean-burn engine in a configuration for combined heat and power (CHP), and demonstrates superior performance compared to the traditional methods. Since our method is based on the physical and chemical processes that govern knock, adapting it to new different engines platforms and fuel compositions is straightforward. For instance, together with a group of key customers, DNV GL is currently applying the method to different engine platforms that use LNG as a fuel (truck, marine and CHP engines).
The user simply enters composition of the pipeline gas mixture as input and the tool calculates a PKI methane number, which can be compared with the requirements of the engine.