Simultaneous decarbonisation of steel and Oil&Gas industry by MSW gasification: Economic and environmental analysis

https://doi.org/10.1016/j.enconman.2021.114577Get rights and content

Highlights

  • The gasification of MSW to hydrogen and reducing gas was successfully simulated.

  • Different scenarios have been analyzed varying energy mix.

  • Energetic analysis returned an overall efficiency of 63.6%

  • Economic analysis returned a payback period of about 6 years.

  • The calculated saving of CO2 was equal to 581 kt/y.

Abstract

The aim of this study is to provide a complete energy, economic and environmental analysis of a waste to chemical process that treats a feed mixture composed of Refused Derived Fuel and Plasmix, transforming it into syngas. The process was implemented in the Aspen Plus® simulation environment, where also a sensitivity analysis returning the maximum value of humidity allowable in three different scenarios of waste mixture has been carried out. Moreover, an economic analysis has been performed in which, on the basis of capital expenditure, operating costs and revenues of the plant, Net Present Value (NPV) and Internal Rate of Return (IRR) has been assessed, finding a value of 599 M€ and 28% respectively. Finally, environmental analysis has been performed; a comparison between the carbon dioxide emissions of the case “as it is now” versus “how it could be” with the waste to chemical process implemented has been carried out in which it was calculated a saving of around 581 kt/y of CO2 emitted in the atmosphere.

Introduction

In the last decade, because of the rapid development of the industrial sectors, the CO2 emissions have reached an alarming level in the atmosphere [1]: in 2019, for the first time in 800,000 years, CO2 concentration in atmosphere has reached the value of 409 ppm; during the last century, this concentration has never exceeded the value of 300 ppm [2]. Similar CO2 concentration levels occurred about 3 million years ago [3], when the temperature was 2–3 °C higher than during the pre-industrial Era and sea level was 15–25 m higher than today [2].

In 2015, the 21st Conference of Parties of the UNFCCC (United Nations Framework Convention on Climate Change) held in Paris with the aim of adopting a new global agreement to limit greenhouse – gas emissions [4]. The attainment of this goal has been considered fundamental to prevent the irreversibility of the global change [5]. The ultimate objective already adopted by governments is to limit global warming to an average of no more than 2 °C, relative to pre-industrial Era [4].

To guarantee this goal, considering the Earth-CO2 absorption ability, the total amount of carbon dioxide emission should not exceed the value of 2900 Gt up to 2100 [6]. However, by 2014, 1900 Gt of CO2 have already been emitted, implying that the remaining budget is only of 1000 Gt. For this reason, according to the UE Climate Action (2050 Long-Term Strategy), all European Countries that adhered to this plan, defined as main objective of the achievement of “carbon neutrality” by the 2050. Moreover, This means that for each ton of CO2 emitted, there should be a ton of CO2 absorbed, by the planet or by any chemical-physical process.

Today, the industry sectors that mainly contribute to CO2 emissions are the iron and steel industry, Oil&Gas, Electric Energy production and transportation [7], [8], [9]. The goal of the near future years is to deal with the energy transition of these areas to reduce their carbon footprint. This can be done by the transition from fossil energy source to renewable sources, such as industrial and municipal wastes, that can be converted in Refuse Derived Fuel (RDF). Starting from this fuel it is possible to produce syngas by gasification-based processes, which is the starting point to produce a vast range of products [10]. This technology, named “Waste to Chemical” (WtC) can be seen as a step forward compared to the “Waste to Energy” (WtE), because all the carbon and hydrogen contained in the waste is converted into a chemical product and not in a flue gas like in the WtE plants.

Various articles in literature reported about the production of a syngas from solid waste, such as the one of Borgogna et al. [11], where an RDF waste has been fed to a gasifier for the production of syngas used for the synthesis of methanol. The RDF was characterized by a composition of combustible fraction (CHO) in a range of 50–80%, a moisture (MOI) of 10–25% and a residual (Ash&OC) of 10–25%; 8 t/h have been fed to a gasifier working at a pressure of 1.2 bar and a temperature that vary from 1600 °C on the bottom to 1100 °C on the top generating a syngas characterized by an appreciable mol% of hydrogen (35%), CO (40%) and CO2 (15%); It was subsequently cleaned and made available for the alimentation to a methanol reactor.

Another study [12] concerns the possibility to use agro-industrial wastes in order to produce fuel gas via catalytic hydrothermal processing. The authors used a reactor of 100 ml of volume, working from 300 to 650 °C and 500 bar. The study reported a produced fuel gas with a composition that depends on temperature: for example, at 300 °C the gas was mostly composed of CO2 (about 90%mol), while at 500 °C the presence of methane and hydrogen (about 45% mol) was predominant.

In this article a “waste to chemical” (WtC) approach has been applied for the reduction of carbon dioxide emissions of two important industrial sectors: Oil Refinery and Steel industry.

The scheme was based on WtC technology and has been applied to two real industrial processes. The main purpose of the process was the reduction of CO2 emissions from the two industrials site by the substitution on one hand of “grey” H2 (the hydrogen produced from a fossil source) with a “circular” H2, produced from wastes that cannot be recycled in other ways and on the other hand of the carbon powder entering in the blast furnace, with a CO-enriched reducing gas, coming from the gasification of mixed solid waste as well. The solid waste taken into consideration, that has to be converted into syngas, consisting of a certain aliquot of Refuse Derived Fuel (RDF) and a remaining part of Plasmix (non-Recyclable plastic). This is subsequently cleaned and separated into a H2 rich stream, and a reducing gas enriched in CO and CO2. The former products can be used as an alternative to the grey – hydrogen, produced from fossil fuels, in the Oil Refinery, whereas the latter stream can be sent as reducing gas in the blast furnace, in substitution of the carbon ash, one of the most polluting agents of the iron and steel industry.

According to the authors’ knowledge, this is the first work that can be applied in a real industrial district as Taranto one, located in Taranto, Italy, dealing with the simultaneous decarbonization of two highly polluting industrial sectors: Oil&Gas and iron/steel industry. This work's novelty consists of the use of a cleaned syngas, obtained from the municipal solid waste (MSW) gasification as starting point to produce green hydrogen and a reducing gas mixture with a low environmental impact. In this article both the technical and economic feasibility and the evaluation of the environmental benefits have been reported, with which the authors evaluated the viability of the proposed scheme inside an actual industrial district.

To sum up, this work aims at evaluating a strategy of energy transition for two fundamental industrial sectors both in Italy and Europe.

Section snippets

Processes description

The process consists in the conversion of the waste mixture composed of RDF and Plasmix (80%-20%), into syngas, which is subsequently divided in hydrogen and a reducing gas composed mainly of CO and CO2.

The waste is fed into a gasification reactor at standard conditions, where is converted in syngas and a granulate that represents the by-product. The gas has to be cleaned in three washing towers, purified from every component that can be dangerous for the natural environment. Finally, the gas

Process simulation

In this section the simulation of the process carried out in the AspenPlus® simulation environment is reported.

The gasification reactor, as it was simulated in Aspen Plus® simulation environment, is reported in Fig. 4. The feed of the plant, identified in the stream MSW in Fig. 4 is composed of 8 t/h of RDF, fed to the bottom of the reactor. The gasifier was modelled as 3 Gibbs reactors that represent the 3 zones in which the reactor can be divided, as reported in a previous work [11]: melting

Economic analysis

An economic analysis to assess the feasibility of the process has been conducted in order to estimate the costs of the plant.

Environmental analysis

The environmental analysis carried out a key role in this study, because, even if it is not a rigorous life cycle analysis, it allows to underline all the advantages of this process, in terms of energy transition and CO2 emissions saving. Indeed, with the waste to chemical process the inlet flowrate of waste can substitute the carbon powder, necessary in the blast furnace for reducing the iron oxides to metal iron.

In this analysis two cases have been considered:

  • The case “as it is now”, that

Simulation results

The results of the cleaning gas section are reported in the Table 11.

Regarding the purification section, as reported in the previous chapter, every reactor was simulated as a separator, in which there was inserted the specifications given by the constructor.

In the Table 12 are reported all the devices necessary to bring the gas composition to the target reported in the Table 13 that allow the gas to be fed in the PSA.Table 14.

Analyzing the reducing gas stream obtained from this process, it is

Conclusions

This work sets in the area of interest of innovative technologies that aims to reduce the emissions of greenhouse gasses from industrial plant and treats the topic of energy transition from fossil fuels to renewable ones. Here the authors studied in detail a possible application of waste to chemical process in an industrial district that would give an important contribute to reduce the carbon dioxide emissions, following the principles of circular economy.

In particular, this project would

CRediT authorship contribution statement

Andrea Liberale Rispoli: Conceptualization, Software, Visualization, Writing - original draft. Gaetano Iaquaniello: Resources, Supervision. Annarita Salladini: Validation, Software. Nicola Verdone: Resources, Supervision. Maria Rosaria Pepe: Validation. Alessia Borgogna: Writing - review & editing, Validation, Software. Giorgio Vilardi: Writing - original draft, Writing - review & editing, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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