Steam, Cogeneration and Efficiency

With all the talk about carbon and renewable energy the largest energy losses often escape the limelight, and we already have the solutions that could be implemented today but decades of infrastructure development and misinformation often block us from making the smarter choice.

Power generating stations were once upon a time, small, and local, often located right on the edge of town.  Now remember at that time the fuel of choice was coal, so as the demand for the new electricity service increased, more coal was burnt in the cities increasing local pollution. Faced with the choice of clean up or move out, the generators moved outside the communities they served to remote locations that allowed larger plants to be constructed, they were out of sight and out of mind.

As the distance between the generator and consumer increased, extra losses in the form of transmission losses occurred, to cover the vast distances the transmission voltage was increased incurring transformer losses at each end of a circuit.

 

Long Transmission Lines Increases losses

Also have you ever wondered why many power generating stations are located near rivers or coastline? Because the process of using steam to electricity generates vast quantities of waste heat, and with the generators now located at distal sites there are few neighbours to use this high grade waste heat so its dumped into the nearest convenient river, cooling tower or seashore.

Inland generators overcome the problem by building cooling towers (pictured below) using vast quantities of water to dump the waste heat into the atmosphere.

Power Generation Cooling Towers

FLICKR http://underclassrising.net/

To be frank the thermal efficiency of a typical coal fired generating station is miserably low approximately 30 -35 percent.

So today, after pushing the generators and pollution away from us, it should not be a surprise to find that less than 10 percent of the energy in fuel ever reaches the consumer or put it another way 90 percent of energy in the fuel is lost forever.

There are viable alternatives for China and elsewhere in Asia. Cogeneration is the engineering term we use, essentially it is a system that will use that waste energy and that means a dramatic efficiency improvement.

The waste heat energy can be used for heating,  process, or air conditioning system and provides an overall thermal efficiency nearer 85 percent,  nearly 300% improvement over conventional plants.

Absorption chillers are a breed apart, they create chilled water but heat energy through a process of concentrating and dilution of spacial salt compounds. High grade waste heat from any source could be used to power air conditioning without the need for large electrical supplies (some electricity would be still needed for the associated air handling units, pumps and automatic controls). 

Local Cogeneration as the name implies is close to the consumer and demands a cleaner fuel, natural gas is a good choice where available.

One barrier for the wider implementation is the utility companies themselves, having invested billions of dollars to build and operate the plant and equipment, they have unsurprisingly created rules to protect that investment.

What is needed is community based approach, for example use the locally created waste to fire cogeneration plants for that community. Instead of hiding from the problem, make it visible, a showcase,  demonstrate that waste from their office or home will be burnt across the street to provide local community electricity.

For manufacturing plants using high pressure steam, a simple design change can result in large benefits, generate superheated steam to drive an electricity turbine first, that will power your factory, and use the turbine exhaust saturated steam to serve your process, and return the condensate to the boiler – its a simple and elegant solution but often overlooked.

Here is a link to an interesting article about the multiple use for steam generation

steam generation and energy efficiency Kelcroft

Instead of using technology, China has sadly followed the western development model for coal fired plant, plus suffering the torment of wasted energy plus regular power outages. Many businesses in China, particularly in Guangdong have no choice except diesel fuelled engines to overcome frequent blackouts and shortages, whilst simultaneously wasting Gigawatts in wasted heat.

Countries with a strong demand for heating homes and offices, such as Germany and Nordic countries in Europe waste heat from power generators is used in district heating systems delivering heat to the doorstep. Here in Asia, and the tropics where air conditioning is demanded for comfort, waste heat from power generators, or biomass boilers should be used to power to absorption chillers.

The public and governments are increasingly focused on demand side awareness, and it is noticeable, through more efficient lighting, LED’s fittings, and air conditioning systems but remember that is one part of the story.  In Hong Kong 1/3rd of the power generated is used to drive air conditioning equipment,  so businesses today are paying utility companies to waste fuel resources that can’t be replenished. Don’t you think it is time to get smart? I do.

John A. Herbert, Kelcroft, Consultant