Brighter energy from unused heat

Cogeneration gets the most from wasted heat

  • Industrial energy efficiency delivers major GHG mitigation opportunities
  • Combined cycle technology captures wasted heat to make more useful energy
  • Cogeneration technology catches even more for other processes

Janet E. Pinheiro |

It is essential we all reduce waste of our carbon constrained planet’s precious natural resources. Industrial energy efficiency is widely regarded as a key priority action toward mitigating climate change.

Greenhouse gas (GHG) emissions are significantly decreased when industry makes the most of its energy-producing fuel. Being frugal with energy also makes good commercial sense.
According to the World Economic Forum, our planet’s manufacturing and production sector is responsible for 20% of global carbon dioxide emissions. The sector also consumes 54% of the world’s energy.

Boosting traditional power generation

Big mitigation impacts happen when industry is smart about its energy use. It makes perfect environmental and business sense when industry captures its unused heat, and converts it into useful energy.

Traditional industrial thermal power production involves producing heat from a carbon-based energy source. The heat boils water to make steam, which is used to drive a turbine.

The turbine drives a generator, and the generator makes electricity. Each power production stage, however, has inefficiencies creating wastefulness.

Super powerful combination

Combined heat and power systems are among the super powers of energy efficiency. They alleviate inefficiency through processes known as combined cycle and cogeneration.

These thrifty systems harness unused heat from an industrial power plant's exhaust stream. Rather than letting the heat escape into the atmosphere, the heat is gathered and used.

The captured heat is put to effective use in the production process. It is a win-win for environment and business.

Less emissions with more

Significant benefits come from the simultaneous production of useful heat and electricity from the same fuel. Less fuel is required to produce more energy; less fuel means less emissions.

Aramco chief engineer Khalid Y. Al-Qahtani said the company's energy efficiency strategy is to achieve 100% self-sufficiency in its operating plants. “Cogeneration systems are key to our strategy of achieving self-sufficiency in electrical power generation and processing heat for our hydrocarbon production facilities,” he said.

Part of the Kingdom’s national utility grid seen on the horizon.

The company is retrofitting existing plants with cogeneration systems to generate as-needed energy on-site, as well as heat for oil and gas production processes. “By producing electricity as a natural byproduct of our operations, we reduce emissions and our energy consumption from the Kingdom's national utility grid,” Al-Qahtani added.

Squeezing the most

Power from combustion turbine-based power plants can be generated by a simple or combined cycle process. In a simple cycle, a combustion turbine produces power but a significant amount of heat is exhausted and wasted.

In a combined cycle, the gas turbine’s waste heat is captured, then used to produce steam, which in turn is used to generate additional electrical power via a steam turbine. As a result, the combined cycle squeezes the most out of a turbine’s fuel, but only satisfies a power production need.

Cogeneration does more than produce additional power. It ensnares the waste heat even a combined cycle cannot capture, and puts it to valuable use.

Instead of wasting steam unsuitable for power generation, cogeneration uses this as heat for other processes. Such as heating a residential complex or supplying heat to a production process.

Aramco’s full-conversion Jazan refinery complex.

Refined environmental thinking

Cogeneration at Aramco, one of the world's largest energy companies, is customized for each particular facility. Each cogeneration plant is closely monitored for any energy surpluses, which are then redirected to other needs, helping to steadily reduce the company's energy intensity.

Aramco's newly built full-conversion Jazan Refinery Complex has an industrial design of leading sensitivity toward environmental protection. The complex — a refinery, gas and power plant — is set up to lower a hydrocarbon's footprint.

Next to the refinery is one of the world's largest integrated gasification combined cycle plants (IGCC), which houses a sizable cogeneration power plant. Clean syngas, produced from vacuum residue piped to the IGCC's gasification plant, energizes a 3.8 GW five-block combined cycle power plant.

The plant's 10 gas and five steam turbines produce power for both the refinery and the national grid, and steam for the refinery's processing production. This super-efficient design is a “smart design” to get the most out of hydrocarbon, and reduce molecular miles.

Lower Industrial carbonization

Improving industrial energy efficiency is a way to quickly and cost-effectively reduce the world’s GHG emission levels. Reducing industrial GHG emissions is integral toward the United Nations successfully achieving the 17 Sustainable Development Goals it adopted in 2015 . The goals address a range of global challenges, and intend to inclusively end poverty, and protect the planet.

Besides cogeneration, recycling waste, diligent maintenance, local sourcing, and carbon capture are among ways to shrink the industry’s carbon footprint.