LDAC systems- Preventing condensate on pipes by dehumidifying air with open absorption systems

In gas pressure regulation and metering stations (GPRMS), natural gas is expanded from a higher to a lower pressure level. The drop in pressure results in a sharp drop in the temperature of the natural gas because of the Joule-Thompson-Effect. To avoid natural gas temperatures that are too low and to prevent condensate on the pipe surfaces, the natural gas is heated before the expansion process. In many GPRMS, the natural gas temperature is kept constant after expansion all year long (e. g. 10°C) This preheating is energetically expensive.

Significant energy savings can be achieved by lowering the gas temperature after the expansion process. The research project is to investigate how this can be achieved by dehumidifying the room air in combination with a dew point control. The expected energy saving potential is large, since the energy requirement for dehumidifying the room air is usually significantly lower than for heating natural gas. The energy saving potential depends on the natural gas flow rate, air humidity, room volume, air exchange rate and the dehumidification technology used.

In the research project, an open liquid desiccant air-conditioning (LDAC) system will be first systematically examined in the laboratory and afterwards tested in the field test at the GPRMS Neu-Eichenberg under real operating conditions for two years. The LDAC system is an innovative pilot plant that uses a hygroscopic liquid (LiCl water solution) to dehumidify the air. The main components of the LDAC system are a dehumidfier, a regenerator and a storage for the salt solution, as well as additional heat exchangers. In the dehumidifier the supply air and the salt solution get directly in contact and due to the vapor pressure gradient the air is dehumidified. The heat released during this process can be removed by cooling water in order to increase the dehumidification capacity. The salt solution, which is diluted by water during the absorption process, is temporarily stored and then concentrated in the regenerator with low-temperature heat (e. g. solar heat (60-80°C)). At the GPRMS Neu-Eichenberg a thermal solar system (135 m²) exists, which already covers part of the natural gas preheating. Since air dehumidification significantly reduces the heat demand for the natural gas preheating, part of the heat demand for the regeneration process of the LDAC system can also be covered by solar energy. All relevant temperatures, humidity, pressures, flow rates and power consumptions are continuously measured during the field test.

On the basis of the laboratory and field test investigations, numerical models of the absorption process and the entire LDAC system will be further developed and validated. The system model of the LDAC system can be used to determine the energy saving potentials based on annual simulations. Furthermore a quantitative comparison of different dehumidification technologies for different boundary conditions will be performed under energetic and economic considerations. The potential of the individual dehumidification technologies depending on the type of application (e. g. GPRMS, greenhouses, swimming pools, agricultural drying, etc.) should be characterized.

The aim of the research project is to develop a technology that leads to significant energy savings in the supply of natural and synthetic gas. In particular, some of the fossil fuels which are used can be substituted by renewable energies (solar heat). Furthermore, the technology can help to prevent corrosion on pipes and moisture damage to the building. The measurement results collected in the research project and the models developed from them should ensure that the concept can be transferred to other GPRMS.

Duration

1.9.2019 - 30.06.2023

Funding

Funded by the European Regional Development Fund Hessen (ERDF).