Making sure that waste recovery doesn’t waste money Environmental protection, recycling, sustainability, reducing CO2 emissions, waste treatment: these are all topics that are at the forefront of 21st century thinking by governments and responsible businesses such as machine makers. But at the heart of any discussion of these issues is the need to ensure that
Making sure that waste recovery doesn’t waste money
Environmental protection, recycling, sustainability, reducing CO2 emissions, waste treatment: these are all topics that are at the forefront of 21st century thinking by governments and responsible businesses such as machine makers. But at the heart of any discussion of these issues is the need to ensure that the solution doesn’t add to the original problem.
Omron recently worked with Italian company Ecodeco to overcome precisely such an issue. Ecodeco is part of Italy’s leading energy group A2A, and specialises in all aspects of designing, making and managing waste-disposal systems. At Corteolona in Lombardy, Ecodeco operates a plant for converting urban waste into refuse-derived fuel (RDF), and a waste-to-energy plant.
RDF is a complex product which has a range of different calorific values depending on the original waste material. At Corteolona, it is fed into the waste-to-energy furnace using a batching system, varying the amount delivered according to its calorific value. At the base of the furnace is 1.5m of sand which is “fluidised” by pumping air in from below: this makes the sand “boil” like a fluid, and mix with the RDF.
8.5MW of electricity from waste materials
This creates a highly combustible mixture which has good heat-exchange distribution and which is used to produce steam to drive a turbine generating about 8.5MW of electricity under normal conditions. As it leaves the turbine, the steam is forced into a cooling tower by a series of 12 fans, where it is converted back to water that is pumped back and recycled through the system.
All of which sounds very “green”.
The issue is that the plant used a lot of electric motors, many operating at high power. There are, for example, twelve 22 kW fans driving the steam into the cooling tower, three 160 kW motors for the pumps sending the cooled water back to the heat generator, and 185 kW motors for each of the two boiler-feed pumps.
The total power requirement used to be 1114 kW, and Ecodeco wanted to reduce this electricity consumption, but without affecting the amount of energy produced. There wasn’t an easy answer, because the three 160 kW motors that send cooled water back to the waste-to-energy plant are about 120m from the electricity distribution board. Ecodeco wanted to use the existing cabling layout, to avoid major excavation work and the cost of new cables.
Simple yet effective
The solution that was developed was simple yet highly effective. Inverters were installed to modulate the frequencies of the different motors while maintaining pressures at a constant level. For the three recirculation pumps, and the two boiler-feed pumps, the inverters simply replaced throttle valves, so there was no need to dig up and replace any of the wiring.
This had zero impact on the plant’s generating capability, but the reduction in power consumption was little short of astonishing, cutting annual electricity usage from 6152 MWh to 5328 MWh – saving almost 100,000€ at current prices. Ecodeco calculated that the total investment would pay for itself within about 13 months.
CO2 emissions reduced by 600 tonnes a year
The energy and financial savings are not the only important aspect of this solution. As the operator of a waste-to-energy plant, Ecodeco is very conscious of its position in the sustainability chain. Generating a single MWh of electricity by conventional methods creates about 725kg of CO2 emissions. So cutting its annual consumption by 824 MWh has the effect of reducing its carbon footprint by almost 600 tonnes.
It’s an excellent demonstration of how to use a supplier’s specialist knowhow to help deliver a relatively simple system which can save energy, cut costs, and help to protect the environment. And all without major construction work or disruption to production.