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MPhil in Engineering for Sustainable Development

global challenges, engineering solutions

Studying at Cambridge

Jenny Garcia

Converting CO2 Waste Streams into Value Added Products A Case Study for Urea and Soda Ash in China

Carbon dioxide is found in numerous gas waste streams throughout the industry and globally approximately 10 giga tonnes per year are released to the atmosphere (Le Quéré et al, 2016).  Approximately 1% of these emissions come from ammonia production (Ammonia Industry, 2017), which is the most common produced chemical and the source of nitrogen based fertilisers like urea and other derivative products such as soda ash, which is used as raw material in glass manufacturing.

Ammonia is mostly produced from hydrogen extracted from hydrocarbons in a process that produces CO2. Its increasing demand follows population growth, putting pressure on the global mitigation initiative for reducing GHG emissions.

Urea and soda ash also require CO2 as feedstock, normally obtained from the CO2 co-produced from hydrogen generation. But, it is contradicting that with so much CO2 released to the atmosphere, CO2 is created as a by-product to be used in urea and soda ash plants.

If ammonia was produced from a non-fossil hydrogen source then CO2 would need to be obtained from a different source e.g. industrial waste stream, creating a market for CO2 utilisation.

This CO2 market gap was the incentive for investigating if it is environmentally and economically practical to produce ammonia from a non-fossil fuel source and utilising carbon capture to manufacture urea and soda ash as downstream options.

To answer the research question, a feasibility assessment was required for comparing the conventional process with the proposed greener scheme. The comparison was made between two options at the same capacity for evaluating CO2 emissions, energy usage, capital and operating costs in a like for like approach.

In terms of geography, the focus is on China, where the market for ammonia, urea and soda ash is predicted to grow and the hydrocarbon source for hydrogen production and for energy is mainly coal, which releases more CO2 than natural gas used in European hydrogen.

China is also investing in renewable energy, opening an opportunity to provide greener energy to industrial processes which are highly polluting such as ammonia.

If future capacity expansion in China follows this approach, urea and soda ash could potentially be a carbon sink for locking CO2 into value added products.

This study opens the opportunity to consider producing these commodities in a more sustainable manner with less dependency on fossil fuels, although it requires a more rigorous assessment of numerous variables will dictate the amount of capital and operating investments based on location.

The alternative process is optimistic in terms of reducing emissions of up to 2 million tonnes per year, but it is financially constrained in CAPEX and OPEX by $117 million and $155million respectively, because of technology efficiency gaps, energy prices and policy that are likely to be reversed in less than 20 years as part of the industrial transition to avoid climate change.