Steam recycling for industrial process heat helps to save energy and costs. In the end, the companies and the environment win.
21. October 2020
Steam recycling

DECARBONIZATION MUST BE THE GOAL

By Dr. Heiko Dittmer
Readtime 4 min.
Keywords #steam compression #environment #heat pump #process heat #energiy efficiency

Table of contents

  • Industrial process heat is still predominantly generated using fossil fuels
  • The pure generation of electricity from waste heat has a poor efficiency
  • A high-temperature heat pump replaces fossil energy with a much smaller proportion of electrical energy
  • Sustainability must be given more focus

Industrial process heat is still predominantly generated using fossil fuels

According to the Federal Statistical Office in Germany, around 650 terawatt-hours of electricity were generated in 2018, of which around 230 TWh were generated using renewable energy sources. But the gap is large, as these figures show.
Whether in endothermic processes, distillation or drying: process heat is the driving force behind industry. Industry accounts for more than a quarter of Germany's total energy consumption, and 70 percent of this is accounted for by the generation of process heat - today mainly fossil.

The pure generation of electricity from waste heat has a poor efficiency

Steam is considered one of the most efficient and flexible energy sources for process heat in industrial production. The chemical industry, food production or paper processing are intensive steam users. Around 150 million tons of steam in the range of 100 °C - 300 °C are generated annually in Germany alone.

Process heat is expensive and waste heat recovery has long been an important issue. Process preheating, building heating or power generation are the common concepts for the subsequent use of industrial waste heat. But - to be honest - this is basically downcycling, because steam has to be produced again for the actual process. Especially the conversion of waste heat into electricity means that most of the heat of evaporation is lost, resulting in poor overall efficiency in relation to primary energy. Often this efficiency is only around 10 percent.

A high-temperature heat pump replaces fossil energy with a much smaller proportion of electrical energy

From the building heating the heat pump principle is well-known. With 1 kilowatt hour of electricity, 4-5 kilowatt hours of heating can be provided. This principle, transferred to industrial processes, offers huge possibilities for improving energy efficiency.

Instead of generating high-pressure steam through a fossil fuel combustion system, existing low-pressure steam can be compressed to process steam pressure using mechanical energy. The required mechanical energy is significantly lower because the heat of evaporation does not have to be re-applied. Under favourable conditions, Coefficients of Performance (COP) above 10 can be achieved.

This high-temperature heat pump thus replaces fossil energy with a much smaller proportion of electrical energy, which will be regeneratively generated in the future. The evaporation heat remains in the process and is not released into the environment.

Sustainability must be given more focus

Spilling Technologies has realized this principle in numerous cases. As in this example: In a paper mill, steam with a pressure of 16 bar and a quantity of 16 tons per hour is required to dry paper sludge. Conventionally, a natural gas-fired steam generator would be used, which consumes 67,200 MWh of gas (and thus also releases around 13,400 tons of CO2 p.a.) during 6,000 operating hours per year.
The waste heat from the drying process provides low-pressure steam at about 3 bar, which is compressed to the process steam level of 16 bar by a high-temperature heat pump (the Spilling steam compressor). Instead of 67,200 MWh/a gas energy, 16,000 MWh/a electrical energy is used. Ultimately, this results in a closed steam cycle that is operated only with the electrical energy for the steam compressor.
In comparison, the conventional gas boiler may be the smaller investment, and gas is also very cheap today. The high temperature heat pump, on the other hand, requires a larger investment. Accordingly, it takes a little longer for this investment to pay off. And yes, too often, quick returns take precedence over sustainability. But we will only be able to successfully master the energy turnaround and the major issues of energy and the environment if we stop using fossil fuels for process heat.
With its products and sophisticated steam technologies, Spilling has been helping for many years to continuously and massively increase energy efficiency in industrial production.
Our experts also have suitable solution proposals for your application.

You can contact us here.

In the production of paper, recycled steam can save a great deal of money.

STEAM-DRIED PAPER BRINGS NOTES

The range of applications for industrial drying is wide: It is used for drying sawdust for pellet production, plants (residues) for animal feed production, pulp drying, sewage sludge drying or the production of wood chips. Often enough, industrial product drying proves to be a very energy-intensive process.

by Angela Kroeger

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