Sweden

Hydrogen is a versatile energy vector for a plethora of applications; nevertheless its production from waste/residues is often overlooked. Gasification and subsequent conversion of the raw synthesis gas to hydrogen are an attractive alternative to produce renewable hydrogen. In this paper recent developments in R&D on waste gasification (municipal solid waste tires plastic waste) are summarised and an overview about suitable gasification processes is given. A literature survey indicated that a broad span of hydrogen relates to productivity depending on the feedstock ranging from 15 to 300 g H2/kg of feedstock. Suitable gas treatment (upgrading and separation) is also covered presenting both direct and indirect (chemical looping) concepts. Hydrogen production via gasification offers a high productivity potential. However regulations like frame conditions or subsidies are necessary to bring the technology into the market.

Due to the small characteristic molecular size of hydrogen small leaks are more common in hydrogen systems compared to similar systems with hydrocarbons. This together with the high reactivity makes an efficient ventilation system very important in hydrogen applications. There are several models available for ventilation sizing that are based on either a well-mixed assumption or a fully stratified situation. However experiments show that many realistic releases will be neither and therefore additional models are needed. One possibility is to use CFD-models but the small release sizes for pinhole releases (<<1 mm) make it difficult to find an appropriate mesh without excessive computational time (especially since the simulations need to be iterated to find the optimum ventilation size). An alternative approach which is described and benchmarked in the current paper is to use a multi-zone model where the domain is divided into several large cells where the mass exchange is simplified compared to CFD and thus simulation time is reduced. The flow in the model is governed by mass conservation and density differences due to concentration gradients using the Bernoulli equation. The release of gas generates a plume which is modelled based on an empirical plume model which gives the entrainment and hydrogen source term for each cell. The model has a short run time and will therefore allow optimization in a short time frame. The model is benchmarked against five experiments with helium at the Canadian Nuclear Laboratories (CNL) in Canada and one hydrogen experiment performed at Lodz University of Technology in Poland. The result shows that the model can reasonably well reproduce accumulation in the experiments with small release without ventilation but appears to slightly underestimate the level of stratification and the interface height for ventilated cases where the source is elevated from the floor level.