Technology steam or a few words about gas turbines in the context of industrial decarbonisation

What is water steam and why do we need it?

Most of us associate water steam with a kettle and the aroma of tea drunk on autumn evenings. For engineers and technologists, steam is the medium that enables heat transfer or provides the driving force for many devices. Water steam is a gas formed when water passes from the liquid state to the gaseous state. At the molecular level, this happens when H₂O molecules manage to break free from the bonds (i.e. hydrogen bonds) holding them together. In liquid water, H₂O molecules are constantly combined and separated. When water molecules are heated, the bonds connecting the molecules begin to break down faster than they can be formed. Eventually, when enough heat is supplied, some molecules will be released. These “free” molecules form a transparent gas that we know as water steam, or more precisely, dry water steam.

Steam applications in industry and power generation

Process steam is used in many industries. Typical steam applications are steam heating processes in factories and industrial plants and powering steam turbines in power plants, but steam applications in industry go far beyond that.

For this article, let’s divide them into:

• Heating/process heat – steam is a low-cost, safe and easy-to-control process medium. Steam heat pipes, thanks to their small diameter, make it easy to deliver heat to various parts of the process. Typical applications include paper mills or rubber processing plants
• Sterilisation – hospitals or process equipment are often recipients of high-temperature steam to clean surfaces as well as neutralise pathogenic microorganisms.
• Propulsion – steam has been used as a driving force since the beginning of the Industrial Revolution, steam engines were used to power railroads, ships and factories. Steam is used as the driving force behind steam turbines to generate electricity in power plants. To improve the efficiency of steam turbines, steam pressure and temperature are raised to higher levels. The steam is in a superheated state before entering the turbine. Steam propulsion is also used to power compressors, pumps, fans, etc.
• Atomisation – various liquid fuels, such as fuel oil, LSHS, and LDO, must be atomised in the burner before combustion. Steam atomization is the process of mechanically separating a liquid into small particles for better combustion. Steam is injected into the fuel to maximise combustion efficiency and minimise soot formation due to underburnt hydrocarbons.
• Humidification – steam is also widely used to raise humidity. Steam is injected into the process, where it adds moisture and heat to the final or prefabricated product. Industrial plants are primarily paper mills and pellet mills.

Emissions and carbon footprint of steam installations

The primary sources of process steam generation in Poland are gas-fired steam or biomass boilers. The first two are typical conventional energy sources. In industry, many obstacles hinder biomass development. The main problem is the very low power density, which involves the need to burn large (by volume) amounts of fuel. Availability and planned changes to the ETS are also not conducive to such investments.

Steam demand is mostly associated with high electricity demand, and EneriaCAT has the perfect response to the challenges of the future. We can generate steam in cogeneration using Caterpillar Solar Turbines gas turbines. In such an application, the turbines show their advantage over gas engines, where steam generation capabilities are limited. The units we offer will not require to be replaced with new ones when hydrogen or biomethane is injected into the gas pipelines. Such a device means a simple reduction of emissions by more than 50% in the case of steam generation in conventional boilers and the purchase of energy from the grid. For most industrial customers we are able to show simple pay-back in 2-3 years, and with subsidies, we further improve this result.

How does a gas turbine generate electricity and steam?

A gas turbine is a device that converts the chemical power contained in the fuel into mechanical (shaft rotation) and thermal (hot exhaust) energy. With additional equipment, mechanical energy can be converted into electricity and heat can be collected as process steam. To set the turbine in motion you need air [1], which is sucked in by the compressor [2], where gas volume is reduced. Compressed air is fed into the combustion chamber [4] where it is mixed with fuel [3] (mains gas, diesel, LPG or biogas). In the combustion chamber [4], the fuel mixture is ignited, and the hot gas resulting from combustion passes through successive turbine stages [5] where it is expanded. The exhaust gas passing through the turbine [5] reduces its pressure and temperature, and its kinetic energy is taken away by the blades, which forces the gas turbine shaft to rotate. The rotating shaft drives a generator [6], thus mechanical energy is converted into electrical energy [7]. Hot exhaust gases with a high mass flow (thermal energy) go to the steam generator [8]. The water that feeds the steam generator is heated by exhaust gases until it boils when a state changes from liquid to gas. In this way, process steam is obtained [9]. The cooled exhaust gases [10] escape into the atmosphere through the chimney.

In situations where the demand for steam is greater than can be generated by the gas turbine, additional afterburning can be used to ensure the desired parameters. If both hot air and steam are needed for technological processes, it is possible to receive thermal energy in two forms simultaneously.

Individual Caterpillar Solar Turbines gas turbines have different process steam generation capabilities.

What do we offer our customers?

Before deciding on such an investment, we will prepare a comprehensive analysis of solutions, help with financing, and prepare a full turnkey budget proposal. We welcome any company or institution looking for real and cost-effective decarbonisation.

mail: jbigoszewski@eneria.pl

Written by: Jakub BIGOSZEWSKI

Gas Turbines Manager, Gas Turbines Expert