An input–output model for energy accounting and analysis of industrial production processes: a case study of an integrated steel plant

Abstract

To promote sustainability, it has become increasingly vital to properly account material and energy flows in industrial production processes. Therefore, a generic process-level input–output (IO) model was developed to provide an integrated energy (material) accounting and analysis approach for industrial production processes. By extending the existing process-level IO models, the production, usage, export and loss of by-products were explicitly considered in the proposed IO model. Moreover, the by-products allocation procedures were incorporated into the proposed IO model to reflect individual contributions of products to energy consumption. Finally, the proposed model enabled calculating embodied energy of main products and total energy consumption under hierarchical accounting scope. Plant managers, energy management consultants, governmental officials and academic researchers could use this input–output model to account material and energy flows, thus calculating energy consumption indicators of a production process with their specific system boundary requirements. The accounting results could be further used for energy labeling, identifying bottlenecks of production activities, evaluating industrial symbiosis effects, improving materials and energy utilization efficiency, etc. The model could also be used as a planning tool to determine the effect that a particular change of technology and supply chains may have on the industrial production processes. The proposed model was tested and applied in a real integrated steel mill, which also provided the reference results for related researches. At last, some concepts, computational issues and limitations of the proposed model were discussed.

Appendix: Embodied energy data of scope 1–3 used in case example

Item	Unit	Embodied energy	Reference	Comments
Iron ores	MJ/t	153	[32]	The energy equivalent of iron ores varies with ore grades, mining technology etc. However, this value is still a good approximation if no other data are available, since the Australian iron ores are the major source for sintering in this integrated steel works
Limestone	MJ/t	67.9	Chinese life cycle Database (CLCD) [31]	Chinese LCI data
Burnt dolomite	GJ/t	4.5	Worldsteel [30]	Applicable if no other reliable data available
Burnt lime	GJ/t	4.5	Worldsteel	Ibid.
Pellets	GJ/t	2.1	Worldsteel	Ibid.
Pig iron	GJ/t	20.9	Worldsteel	Ibid.
Steel scrap	MJ/t	8.4	CLCD	Chinese LCI data
Electricity (coal)	GJ/MWh	9.41	National statistical report and standards	As suggested by national standard, the embodied energy of electricity is calculated based on coal consumption of electricity supply, i.e., 0.321 tce/MWh in the year 2013a
Washed coal	GJ/t	27.59	National statistical report and standards	Calculated based on China Statistical Yearbook (Using a conversion factor of 1.047 GJ/GJ)
Anthracite	GJ/t	21.9	National statistical report and standards	Ibid.
Coke	GJ/t	34.1	Worldsteel	Applicable if no other reliable data available
Oxygen	GJ/(103 m3 s.t.p.)	3.25	Site value	Data are sourced from supplier
Argon	GJ/(103 m3 s.t.p.)	15.82	Site value	Ibid.
Nitrogen	GJ/(103 m3 s.t.p.)	1.79	Site value	Ibid.
COG	GJ/(103 m3 s.t.p.)	17.06	Site value	Avoiding heat production through fossil fuels
BFG	GJ/(103 m3 s.t.p.)	3.70	Site value	Ibid.
BOF gas	GJ/(103 m3 s.t.p.)	6.25	Site value	Ibid.
BF slag	GJ/t	1.88b	Calculation based on Refs. [34] and [35]	Avoiding 0.9 tonne cement clinkers per tonne of BF slag
BOF slag	MJ/t	11.59	Ref. [33]	Avoiding production of aggregate. Here, we use energy consumption data of aggregate production in Serbia, since the local data are not found
Benzol	GJ/t	41.88	Site value	Avoiding Benzol production
Coal tar	GJ/t	37.69	Site value	Avoiding coal tar production
Ammonium sulfate	GJ/t	24.38	CLCD	Avoiding ammonium sulfate production
CDQ steam	GJ/GJ	1		Avoiding steam generation. Here we assume avoiding 1 GJ steam production with the same heat quality per GJ CDQ steam
Sinter steam	GJ/GJ	1		Ibid.
BOF 1 steam	GJ/GJ	1		Ibid.
BOF 2 steam	GJ/GJ	1		Ibid.
BOF 3 steam	GJ/GJ	1		Ibid.
Power plant steam	GJ/GJ	1		Ibid.
TRT electricity	GJ/MWh	9.41	National statistical report and standards	Avoiding electricity production

1. ^aThe tce (tonne of standard coal equivalent) is an energy unit used in China, which is equal to 29.307 GJ
2. ^bThe blast furnace slag is used to produce cement as substitution of cement clinkers produced with large rotary kiln. 1 kg of BFS is assumed to replace 0.9 kg cement clinkers. The embodied energy of cement clinkers is 3.84 GJ/t while the slag treatment process consumes 1.58 GJ energy per ton of BF slag. The net credit is therefore calculated as $3.84 \times 0.9 - 1.58$, which is equal to 1.88 GJ per ton (BF slag)