Self-supplier with a small footprint

Article Chemie Technik, 11/21

New technologies in nitrogen production

On site self production is an environmentally friendly and at the same time inexpensive way of supplying nitrogen. With new hydrogen and heat recovery technologies, the balance can be improved even further.

In the chemical and oil and gas industries, nitrogen (N2) is used as an inert and process gas to avoid fires and explosions as well as undesirable oxidations. Nitrogen generators allow companies to produce the gas themselves on site. With the help of pressure swing adsorption technology (PSA), oxygen and CO2 are adsorbed from the ambient air and the production of a continuous flow of N2 in the desired quantity and quality is ensured.

Compressed air factor as the greatest lever

The compressed air required for this is generated by compressors - a process that is energy-intensive, as a significant part of the amount of electricity supplied is converted into heat. This amount of heat can be used decentrally in a gas generation waste heat concept in order to substitute fossil fuels for the provision of heat (and cold). By using the waste heat, not only can gas be provided economically, but the company's CO2 footprint can also be permanently reduced.

Which specific options are available for companies to reduce their own CO2 footprint when producing their own nitrogen and at the same time save energy and costs? When producing nitrogen in-house using PSA technology, the air compressor is the largest energy consumer to provide the required amount of compressed air. The so-called compressed air factor indicates which compressed air volume is required to produce an equal volume of nitrogen (e.g. with a purity of 99.999%). Thus, the greatest lever for lowering the CO2 footprint is to reduce the compressed air requirement.

Hydrogen reduces oxygen levels

By optimizing the earlier design of the PSA technology, a significant reduction in the compressed air factor has been achieved since 2017. However, this was only an intermediate step, because the development of Inmatec's Kat system and the addition of hydrogen made it possible to further reduce the compressed air factor. With the help of the hydrogen catalyst, the "raw" nitrogen (purity 99.5 - 99.9%) obtained via the nitrogen generator is enriched with tiny amounts of hydrogen and catalytically converted, which reduces the residual oxygen content and a purity of 5.0 or higher can be achieved. In this way, larger quantities of high-purity nitrogen can be produced with a significantly reduced compressed air requirement (compressed air factor from 2.9), whereby up to 70% of the amount of energy used in previous PSA technologies can be saved.

Table: Compressed air factor in various PSA technologies

Waste heat can be used

Another way to reduce the carbon footprint in self-production of nitrogen is to use the waste heat that can be recovered from the air compressor. Heat recovery technologies make it possible to use the resulting waste heat in the form of warm air or hot water for heating rooms and for process heating. Both screw compressors and compressed air heating power stations are suitable for this. Using special technologies for combined heat, power and cooling, it is also possible to convert the heat generated by the compressed air heating power station into cold. Excess heat that cannot be used in summer, for example, can be used to cool rooms and processes. By using the waste heat, usually fossil fuels such as natural gas, LPG or oil can be replaced in industrial companies, which has a positive effect on the direct CO2 footprint.

Public funding creates incentives

The Federal Office of Economics and Export Control (BAFA) supports companies in such initiatives by promoting energy efficiency and process heat from renewable energies in the economy. The decisive factor for the calculation is the resulting CO2 saving that is achieved through the investment. Depending on the size of the company, the funding amounts to 500 to 700 euros per ton of CO2 saved annually. For this purpose, the energy consumption of an energy-saving system is compared to a "normal" nitrogen generation system.

An example: If the CO2 saving achieved amounts to 154 t, this secures the company BAFA funding of 107,800 euros. This is paid to the company as a non-repayable grant. The company described in this example continues to reduce its costs by 55%, taking hydrogen costs into account, thus permanently saving 63,000 euros per year. The use of additional heat recovery technology can also reduce heating costs. In this case, these savings amount to a further 18,400 euros per year. In total, there is an economic cost reduction of 81,400 euros per year. Modern systems for self-generation of nitrogen can thus contribute to lowering costs and at the same time reducing the CO2 footprint.

Example: Comparative calculation for applying for funding

Published in Chemie Technik 11/21