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.

Cutting Oxygen Production-Related Greenhouse Gas Emissions by Improved Compression Heat Management in a Cryogenic Air Separation Unit

Oxygen production in cryogenic air separation units is related to a significant carbon footprint and its supply in the medicinal sphere became critical during the recent COVID-19 crisis. An improved unit design was proposed, utilizing a part of waste heat produced during air pre-cooling and intercooling via absorption coolers, to reduce power consumption. Variable ambient air humidity impact on compressed air dryers’ regeneration was also considered. A steady-state process simulation of a model 500 t h−1 inlet cryogenic air separation unit was performed in Aspen Plus® V11. Comparison of a model without and with absorption coolers yielded an achievable reduction in power consumption for air compression and air dryer regeneration by 6 to 9% (23 to 33 GWh year−1) and a favorable simple payback period of 4 to 10 years, both depending on air pressure loss in additional heat exchangers to be installed. The resulting specific oxygen production decrease amounted to EUR 2–4.2 t−1. Emissions of major gaseous pollutants from power production were both calculated by an in-house developed thermal power plant model and adopted from literature. A power consumption cut was translated into the following annual greenhouse gas emission reduction: CO2 16 to 30 kilotons, CO 0.3 to 2.3 tons, SOx 4.7 to 187 tons and NOx 11 to 56 tons, depending on applied fossil fuel-based emission factors. Considering a more renewable energy sources-containing energy mix, annual greenhouse gas emissions decreased by 50 to over 80%, varying for individual pollutants.

Investigation of Air Extraction and Carbon Capture in an Integrated Gasification Combined Cycle (IGCC) System

Coal is one of the major sources of energy currently as it provides up to 38.5% of the total electricity produced in the world. Burning coal produces pollutants and large amounts of CO2, which contribute to climate change, environmental pollution, and health hazards. Therefore, it is our obligation to utilize coal in a cleaner way. Cleaner coal energy can be produced by using an ultra-supercritical Pulverized Coal (PC) power plant, or by employing the Integrated Gasification Combined Cycle (IGCC). Since the 1970s, the IGCC technology has been developed and demonstrated, but it has still not been widely commercialized. One of the methods to improve IGCC performance is to save the compression power of the air separation unit (ASU) by extracting the compressed air from the exit of the gas turbine as a portion of or the entire air input to the ASU. This paper investigates the effect of various levels of air integration on the IGCC performance. The results show that a moderate air integration ranging from 15% to 20% provides the most effective air-integration. An analysis of implementing a sour-shift pre-combustion carbon capture results in a significant loss of about 5.5 points in efficiency. This study also provides the effect of air integration and carbon capture on emissions including NOx, SOx, CO2, and water consumption.