Full oxygen blast furnace steelmaking: From direct hydrogen injection to methanized BFG injection

This paper presents a novel concept of Power to Gas in an oxygen blast furnace, through blast furnace gas methanation and direct H2 injection. The PEM electrolyser produces H2, which reacts with the CO and CO2 from the blast furnace gas forming synthetic natural gas. The latter gas is injected into the blast furnace, closing a carbon loop and avoiding CO2 emissions. A parametric analysis is performed to vary the H2:CO2 ratio in the methanation reaction. Different ratios are simulated and compared, among of which the most representative are: (i) 2.5, where unreacted CO2 is directly recycled with the synthetic natural gas; (ii) 4, where stoichiometric conditions are found and the synthetic gas is composed mostly by CH4; and (iii) 8, where an excess of H2 is found in the synthetic gas; and (iv) an infinite ratio, where only H2 is injected in the blast furnace. In the latter, the methanation plant is not required, and no synthetic natural gas is produced. The results show that low H2:CO2 ratios perform poorly, involving high PEM sizes and high costs but only a 5% of CO2 avoidance (compared to conventional blast furnaces). A H2:CO2 ratio of 4 and full H2 injection results in higher reduction of CO2 emissions (33.8 % and 28.6%) with carbon abatement costs of 260 and 245 €/tCO2, respectively

Limits on the integration of power to gas with blast furnace ironmaking

This article compares 16 Power to Gas integrations for blast furnace ironmaking by using 17 key performance indicators. The study includes 4 types of PtG (PtH2, PtSNG using pure CO2, PtSNG using treated BFG, and PtSNG using BFG), two types of blast furnaces (air-blown and oxygen) and two types of fossil replacement (coal or coke). The blast furnaces are modelled using the Rist diagram, validated with literature data (<2% deviation). For most cases, the decrease in total CO2 emissions is around 150–215 kgCO2/tHM per MW/(tHM/h) of electrolysis. The energy penalty (in terms of electricity consumption) was found to be mostly independent on the size of the PtG plant, but greatly dependent on the type of integration (10.1–20.6 MJ/kgCO2). If significant CO2 reductions are aimed, self-sufficiency in electricity consumption will not be achieved. In practice, the maximum PtG capacity to install is limited by the decrease in the flame temperature. In this context, the PtSNG integration consuming treated BFG, applied to OBF for coal replacement, provides the best results. Assuming a 500 tHM/h blast furnace, the PtG capacity of this concept could be as large as 490 MW and avoid up to 21% of the CO2 emissions

Revisiting the Rist diagram for predicting operating conditions in blast furnaces with multiple injections

Background: The Rist diagram is useful for predicting changes in blast furnaces when the operating conditions are modified. In this paper, we revisit this methodology to provide a general model with additions and corrections. The reason for this is to study a new concept proposal that combines oxygen blast furnaces with Power to Gas technology. The latter produces synthetic methane by using renewable electricity and CO2 to partly replace the fossil input in the blast furnace. Carbon is thus continuously recycled in a closed loop and geological storage is avoided. Methods: The new model is validated with three data sets corresponding to (1) an air-blown blast furnace without auxiliary injections, (2) an air-blown blast furnace with pulverized coal injection and (3) an oxygen blast furnace with top gas recycling and pulverized coal injection. The error is below 8% in all cases. Results: Assuming a 280 tHM/h oxygen blast furnace that produces 1154 kgCO2/tHM, we can reduce the CO2 emissions between 6.1% and 7.4% by coupling a 150 MW Power to Gas plant. This produces 21.8 kg/tHM of synthetic methane that replaces 22.8 kg/tHM of coke or 30.2 kg/tHM of coal. The gross energy penalization of the CO2 avoidance is 27.1 MJ/kgCO2 when coke is replaced and 22.4 MJ/kgCO2 when coal is replaced. Considering the energy content of the saved fossil fuel, and the electricity no longer consumed in the air separation unit thanks to the O2 coming from the electrolyzer, the net energy penalizations are 23.1 MJ/kgCO2 and 17.9 MJ/kgCO2, respectively. Discussion: The proposed integration has energy penalizations greater than conventional amine carbon capture (typically 3.7 – 4.8 MJ/kgCO2), but in return it could reduce the economic costs thanks to diminishing the coke/coal consumption, reducing the electricity consumption in the air separation unit, and eliminating the requirement of geological storage

Modelling calcium looping at industrial scale for energy storage in concentrating solar power plants

Ca-Looping represents one of the most promising technologies for thermochemical energy storage. This process based on the carbonation-calcination cycle of CaO offers a high potential to be coupled with solar power plants for its long-term storage capacity and high temperatures. Previous studies analyzed different configurations of CaL integrated into power cycles aiming to improve efficiency. However, most of these assessments based on lumped models did not account for scale effect in the most critical reactor. In this work, a detailed 1D-model of a large-scale carbonator is included in the comprehensive model of the integrated facility. The results obtained served to assess the available heat, the minimum technical part load of this equipment, the required size of the storage tanks and the overall efficiency of the plant. The main issue in the operation of large-size carbonator is the heat removal, thus a multi-tube internally cooled reactor is proposed. The designed carbonator provides 80 MWth at nominal operation and 40 MWth at minimum part load operation. The sizing of storage tanks depends on the operation management, ranging between 5,700-11,400 m3 for 15 hours. Different efficiencies of the system were defined and presented through operating maps, as a function of the reactor loads

Design and operational performance maps of calcium looping thermochemical energy storage for concentrating solar power plants

Calcium-looping thermochemical energy storage associated to concentrating solar plants appears as promising technology given its potential to increase the storage period and energy density of the stored material. Up to now, research efforts focused on the global efficiency of the TCES associated to different power cycles under fixed modes of operation: day or night. However, TCES will never operate under a stationary situation but will experience different operation points to adapt to solar availability and energy demand from the power cycle. The aim is to analyse the influence of those variables which define the operation points, under energy storage and release modes, in the design of the heat exchangers network, storage tanks and reactors involved in the TCES system. The equipment in the conceptual plant have been modelled accounting variable storage/discharge fractions in the mass balances. The results show a suitable capture efficiency, quantifies the stored power and define the size and performance of the heat exchangers required to operate the system. The behaviour of each heat exchanger and their relevance in heat integration with a power plant is derived. The novelty relies in the analysis of potential situations arising from different combinations of charge/discharge fractions of storage tanks

Improved Flexibility and Economics of Combined Cycles by Power to Gas

Massive penetration of renewable energy in the energy systems is required to comply with existing CO2 regulations. Considering current power pools, large shares of renewable energy sources imply strong efficiency and economic penalties in fossil fuel power plants as they are mainly operated to regulate the system and constant shutdowns are expected. Under this framework, the integration of a combined cycle power plant (CCPP) with an energy storage technology such as power to gas (PtG) is proposed to virtually reduce its minimum complaint load through the diversion of instantaneous excess electricity. Power to gas produces hydrogen through water electrolysis, which is later combined with CO2 to produce methane. The main novelty of this study relies in the improved flexibility and economics of combined cycles by means of using power to gas as a tool to reduce the minimum complaint load. The principal objective of the study is the quantification of cost reduction under different scenarios of shutdowns and conventional start-ups. The case study analyses a combined cycle of 400 MWe gross power with a minimum complaint load of 30% that can be virtually reduced to 20% by means of a 40- MWe power-to-gas plant. Eight scenarios are defined to compare the reference case of conventional operation under hot, warm, and cold start-ups with power-to-gas-assisted operation. Additionally, PtG-assisted operation scenarios are analyzed with different loads (30–50–70%). These scenarios also include the consideration of a temporary peak of demand occurring in a period in which dispatch is below the minimum complaint load. Under this situation, the response time of conventional plants is very limited, while PtG-assisted CCPP can rapidly satisfy the peak. The techno-economic model quantifies the required fuel, gross and net power, and emissions as well as total costs and incomes under each scenario and net differential profit in an hourly basis. The analysis of the obtained results does not recommend the operation of the PtG-assisted CCPP at minimum complaint load for hot, warm, or cold start-ups. However, important marginal profits are achieved with the proposed system for part-loads operation over 50% for every sort of start-up, avoiding shutdowns and extending the capacity factor

A review on CO2 mitigation in the Iron and Steel industry through Power to X processes

In this paper we present the first systematic review of Power to X processes applied to the iron and steel industry. These processes convert renewable electricity into valuable chemicals through an electrolysis stage that produces the final product or a necessary intermediate. We have classified them in five categories (Power to Iron, Power to Hydrogen, Power to Syngas, Power to Methane and Power to Methanol) to compare the results of the different studies published so far, gathering specific energy consumption, electrolysis power capacity, CO2 emissions, and technology readiness level. We also present, for the first time, novel concepts that integrate oxy-fuel ironmaking and Power to Gas. Lastly, we round the review off with a summary of the most important research projects on the topic, including relevant data on the largest pilot facilities (2–6 MW)

Decision-making methodology for managing photovoltaic surplus electricity through Power to Gas: Combined heat and power in urban buildings

Power to Gas technology, which converts surplus electricity into synthetic methane, is a promising alternative to overcome the ¿uctuating behavior of renewable energies. Hybridization with oxy-fuel combustion provides the CO2 ¿ow required in the methanation process and allows supplying both heat and electricity, keeping the CO 2 in a closed loop. The complexity of these facilities makes their management a key factor to be economically viable. This work presents a decision-making methodology to size and manage a cogeneration system that combines solar photovoltaic, chemical storage through Power to Gas, and an oxy-fuel boiler. Up to 35 potential situations have been identi¿ed, depending on the surplus electricity, occupancy of the intermediate storages of hydrogen and synthetic methane, and thermal demand. For illustration purposes, the methodology has been applied to a case study in the building sector. Speci¿cally, a building with 270 kW of solar photovoltaic installed power is analyzed under nine energy scenarios. The calculated capacities of electrolysis vary from 65 kW to 96 kW with operating hours between 2184 and 2475 h. The percentage of methane stored in the gas grid varies from 0.0% (no injection) to 30.9%. The more favorable scenarios are those with the lowest demands, showing temporary displacements beyond the month between injection and utilization

Techno-economic feasibility of power to gas–oxy-fuel boiler hybrid system under uncertainty

One of the main challenges associated with utilisation of the renewable energy is the need for energy storage to handle its intermittent nature. Power-to-Gas (PtG) represents a promising option to foster the conversion of renewable electricity into energy carriers that may attend electrical, thermal, or mechanical needs on-demand. This work aimed to incorporate a stochastic approach (Artificial Neural Network combined with Monte Carlo simulations) into the thermodynamic and economic analysis of the PtG process hybridized with an oxy-fuel boiler (modelled in Aspen Plus®). Such approach generated probability density curves for the key techno-economic performance indicators of the PtG process. Results showed that the mean utilisation of electricity from RES, accounting for the chemical energy in SNG and heat from methanators, reached 62.6%. Besides, the probability that the discounted cash flow is positive was estimated to be only 13.4%, under the set of conditions considered in the work. This work also showed that in order to make the mean net present value positive, subsidies of 68 €/MWelh are required (with respect to the electricity consumed by PtG process from RES). This figure is similar to the financial aids received by other technologies in the current economic environment

Lab-scale experimental tests of Power to Gas-Oxycombustion hybridization: system design and preliminary results

Power-to-Gas (PtG) represents one of the most promising energy storage technologies. PtG converts electricity surplus into synthetic natural gas by combining water electrolysis and CO2 methanation. This technology valorises captured CO2 to produce a ‘carbon neutral’ natural gas, while allowing temporal displacement of renewable energy. PtG-Oxycombustion hybridization is proposed to integrate mass and energy flows of the global system. Oxygen, comburent under oxy-fuel combustion, is commonly produced in an air separation unit. This unit can be replaced by an electrolyser which by-produces O2 reducing the electrical consumption and the energy penalty of the carbon separation process. The aim of this work is to present the design, construction and testing of a methanation reactor at laboratory scale to increase the knowledge of the key component of this system. Experimental data are used to validate the theoretical kinetic model at different operating temperatures implemented in Aspen Plus. CO2 conversions about 60-80% are found for catalyst temperature between 350 and 550 ºC. These values agree well with expected theoretical conversions from the kinetic model