Decarbonisation Technology - February 2022 Issue

de-NOx, de-SOx, or dedusting. Pollution control is an absolute necessity for the well-being of people. CO 2 is more ethereal – if I can use that word – but by putting a cost on it (being through a market, tax credit, renewable/low carbon fuel standards), it allows the industry to potentially benefit. Two examples are:  CO 2 can be injected in concrete to cure it and at the same time embed some CO 2 into it.  Alternatively, CO 2 electrolysis or CH 4 plasma pyrolysis produce pure carbon that can be transformed into graphene, which when mixed with concrete increases its performance (compressive strength). Graphene is a one- atom-thick graphite sheet created from elemental carbon. As modern plants become ever more efficient, the waste heat available tends to diminish. Voluntarily degrading the efficiency of a plant to recover more heat is only practised in countries where the electrical grid is so unreliable that the plants have to produce their own electricity. It is still an inefficient solution, since a gas turbine exhaust temperature is around 550°C compared to 350°C in cement plant flue gas.

The actual payback of such a WHR project is usually closer to three to eight years, which puts them outside the common two years most plants use as the limit for investing in upgrade projects. It could vary greatly, of course, depending on the size of the plant, the flue gas flow/temperature, and the price of electricity (or rather the structure of the electricity tariff applicable to the plant, as with the increase of intermittent renewable electricity penetration, the tariffs have ever more levels – seasonality, peak time, load charges, interruptibility clauses). Another parameter is the operating flexibility, or lack of, for a given process. A float glass furnace, for instance, must run for five to seven years without interruption. An EAF steel plant is a batch process with a 60-minute cycle. A cement plant can be shut down and restarted at some cost, and while clinker production is 24/7, actual cement production, which mostly consists of milling, can be programmed to match low electricity price times. Third-party finance This is where third-party financing companies intervene. Some of are purely project financiers, others are more encompassing and offer a full Energy-as-a-Service (EaaS) solution, and soon

The project

• Heat recovery on the annealing line of a steel factory • Three-quarters of the recovered heat is used by the steel plant itself for space heating and process needs • The remaining heat is supplied to the neighbouring district heating network

Kyotherm

Key data

• Annual heat recovery: 41 000 MMBTU per year • Commissioning date: October 2018 • 10-year Energy-as-a-Service contract • CO 2 savings: 4,000 tons per year • Construction cost: $7m

Waste heat recovery on a steel factory

Source: KYOTHERM