D1B.4 Dust transport properties of hydrogen and natural gas in filters of gas stations

In view of the energy transition, there is an ongoing interest to assess whether the existing natural gas infrastructure can be utilized to transport hydrogen. In the HyDelta work package 1B, it is specifically researched if existing gas pressure reducing stations are suitable, or alternatively can be made suitable for this purpose. One of the focus area’s in a gas pressure reducing station is the filter element. This filter element is applied to filter the incoming gas and remove dust and protect the active components of the station as well as the downstream grid.

In the past, Kiwa has performed research into the gas transport velocity [1] where it was concluded that in case of hydrogen, a factor 3 will be applicable to be able to transport the same amount of energy. The effect of this increase in gas velocity on the filter is unknown. Therefore the main goal of this research will be to answer the following question:

Is it possible to utilize the currently applied type of filter element without modifications to safely and efficiently filter dust in the natural gas grid when hydrogen would be applied?

An answer on the main question contains many aspects and cannot be answered clearly without understanding the basic physics of dust transport in a hydrogen environment. To understand and answer the basic physics, the following sub-questions have been drafted. Sub-questions 1 to 4 will be answered in this report, questions 5 and 6 will be researched in a follow up;

1. What is the consequence of switching from natural gas to hydrogen in view of the gas velocity and the effects on dust transport?
2. Will the increase in gas velocity lead to an increase of dust in the filters?
3. Which characteristics of the dust in the natural gas grid are important to take into account when executing the test program?
4. Which variables should be examined in test program to assess the risk involved with respect to the transportation ability of dust when switching from natural gas to hydrogen?
5. What is the effect of operational gas grid pressure on dust transport?
6. What are the consequences for the filters with respect to dust transport?

The sub-questions are aimed so to give insights into the transport of dust in natural gas as well as in hydrogen. The main question can be answered by the sub-question if two assumptions are made. Firstly; the change in medium from natural gas to hydrogen has little to no effect on the filtration properties of the filter. Secondly: the impact of the particles that hit the filter is negligible compared to the mass and rigidity of the filter. By doing so, the main question can be simplified by answering a part of the sub-questions.

To answer the sub-questions, a literature study was executed. As a result, several theories were found but none of these include research involving dust transport phenomena with hydrogen. To examine which theory approaches reality, a set of experiments have been performed. The literature study was used as a basis to practically approach the construction of a test setup. With this transparent setup, tests have been performed in 6 steps. In the first set of tests, the reproducibility as well as the dependency of time and mass have been mapped. The tests will support the selections which were made to perform the second set of tests.

The terminal velocity (defined as the tipping point where a dust particle start to move with the gas) in relation to the dust particle size were researched for air, natural gas and hydrogen. From these experiments, it can be concluded that the terminal velocity is between 1,2 and 2,6 times higher for hydrogen in comparison with natural gas. When this is combined with the knowledge that hydrogen needs an increased velocity by a factor of 3, it can be concluded that it is likely that initially more dust will be transported if the grid is transferred to the distribution of hydrogen. This is the most important conclusion from these test. The biggest nuance on this conclusion is that dust transport is dependent on the mean dust particle size as well as the density of the dust.

This research indicates that there seems to be a link between the momentum (rho-v²) of the gas and the amount of dust which is moved. A recommendation here would be to further examine this momentum theory experimentally as well as theoretically. Understanding this link could be an enabler to understand dust transport phenomena in different gasses as well as dust transport with gasses at different pressures. Also it is recommended that tests with actual stations, pressures and flows are preformed to validate the models and assumptions.