(485h) Process Design and Operation for the Flexible Electrification of Methanol Synthesis

The US chemical industry consumes roughly 7,000 trillion BTU of energy annually, accounting for more than 10% of total energy consumption in 2018 [1]. Avoiding generating carbon dioxide during the production of feedstocks (such as hydrogen) is key for mitigating the carbon footprint of the chemical industry [2]. It is estimated that the global warming potential (GWP) of producing one kg of hydrogen by methane steam reforming is 11.8 CO2-equivalent kg [3]. Instead of using steam reforming, sourcing hydrogen from splitting water by using renewable electricity enables reduction of carbon emissions.

Producing chemical feedstocks from renewable (e.g., wind/solar) electricity paves the way to decarbonization. Moreover, this is one of the most promising methods for helping balancing the supply and demand of the power grid [4,5]. For example, using electrolyzers, electricity can be used to spilt water and synthesize hydrogen, which can then be used as a feedstock for chemical production. Using electricity through water electrolysis and synthesizing hydrogen together with CO/CO2/N2 into gaseous or liquid, enables the integration of electricity and chemical sectors [6]. This Power-to-X concept has been applied to a host of chemical processes including the synthesis of ammonia [7-10], methane [11-14], methanol [15-19], Fischer-Tropsch liquids [20-22], and dimethoxymethane (DME) [23-24]. Unfortunately, techno-economic analysis (TEA) studies show that approach is not cost-competitive with traditional fossil fuel-based methods [24-27]. At present, 60-70% of the current electrolytic hydrogen cost is due to electricity demand [27]. Consequently, the economic viability of these technologies heavily depends on the electricity cost.

In 2020, the average wholesale electricity price in the US was 21.03$/MWh. In the mid regions like Kansas, Oklahoma, and Texas, the average wholesale electricity price was between 13.6-19.04$/MWh [28]. Moreover, electricity markets are quite volatile; for example, the electricity price of the real-time market (RTM) changes widely every 15 mins and negative prices are common [28]. The presence of negative prices implies that facilities can be remunerated for consuming electricity. Low electricity prices, high frequency of negative prices, and the volatile nature of energy markets bring new opportunities to the chemical production systems that require hydrogen as input. To harness these features of the current energy market, we propose a computational framework that facilitates the optimal design and operation of flexible electrification coupled with chemical production systems. The goals of our framework are:

• Decipher the economic feasibility of retrofitting an existing chemical production system with a flexible electrification unit.
• Investigate the impact of some key technological and economic parameters on the viability of this strategy.
• Identify the optimal design and the operation mode of the proposed infrastructure.
• Reveal the Levelized hydrogen production cost under variable electricity markets.
• Discuss how should chemical facilities participate in a dynamic electricity market by using flexible electrification.

To achieve these goals, we developed a multi-period linear optimization model that facilitates the optimal sizing and operation of a flexible hydrogen production systems that respond to volatile electricity market signals. We applied this framework to study the economic potential of electrification of methanol synthesis; our analysis reveals that real-time electricity price dynamics provide incentives that make electrification economically viable.

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