Successful energy transformation requires highly efficient energy-producing systems and sustainability governance of energy resources. Currently, several ecological and economic reasons exist for opting for biomass fuel for electricity and heat production. Bioenergy is also a potentially sustainable and affordable alternative and complement to fluctuating renewable energy resources. Key aspects to efficient bioenergy production are efficient fuel supply, modern combustion technologies, and the complex efficiency of energy-generating units.
BIOMASS IS THE FUEL OF THE FUTURE
Biomass is the biodegradable fraction of plant and animal substances derived from by-products, waste and residues of agriculture, forestry, and fishing, including the organic components of industrial and municipal waste. Biomass production is based on solar activity, so it is commonly classified as a renewable source. One of the main advantages of using biomass for energy production is the low concertation of pollutants. More particularly, the minimum content of SO2 in the flue gas and the neutral amount of CO2. Biomass combustion emits the same amount of carbon, which was absorbed during the growth of the used organic material, so it does not contribute to the greenhouse effect and connected climate change and other ecosystem impacts.
Another aspect that justifies biomass combustion as an efficient technological solution is the local availability of fuels. It is possible to use various resources as fuels in a single electricity or heat producing plant. Also, the by-products of other industrial processes may be used as fuels with no need for further processing. The ability to utilise easily available fuels constitutes the prevailing financial incentives for developing new power and heating plants. The majority of biofuels used for energy production is derived from wood waste, process residues and the biological fraction of waste. Agricultural produce and waste make up the bulk of resources for the production of liquid biofuels.
State legislative frameworks also support these technologies regarding the advantages mentioned above, thanks to which state support for the implementation of facilities using biomass is available. In the Czech Republic, it is currently possible to participate in, for example, HEAT or ENERG ETS subsidy programs administered by the State Environmental Fund of the Czech Republic. This grant support is financed through the Modernization Fund. It is part of the European strategic package - the Green Deal and represents one of the instruments contributing to the EU's transition to a more sustainable economy. Approximately CZK 150 billion is allocated for the Czech Republic, which represents 15.6% of the total resources of the Modernization Fund. This fund intends to support 10 EU Member States with lower-level income. It is a substantial part of the support system to accomplish the vision of making Europe the world's first climate-neutral continent by 2050.
Concerning technological breakthroughs increasing the efficiency of energy production and expanding the possibilities of efficient distribution of electricity, ecological regulation and rising prices of fossil fuels, an increase in the share of biomass in the energy mix is inevitable. The IEA (2020) forecast predicts a doubling of the amount of biomass consumed for energy production in the next decade under the IEA Sustainable Development Scenario (SDS – which sets a global development trajectory to achieve the main goals of sustainable energy development).
The PBS hot-water biomass boiler with flue gas condensation in the Olsztyn heating plant is supplying 25 MW of thermal energy at a consumption rate of 8.5 - 15.7 tonnes of biomass per hour, depending on the calorific value of the fuel. Fuel feed is provided by sliding hydraulic floors, belt conveyors and through a reservoir directly to the boiler. Flue gases are cleaned by a fabric filter and a condensing heat exchanger is placed before the chimney inlet, increasing the overall system efficiency by 5.1% to a total of 96.6%.
BIOMASS COMBUSTION TECHNOLOGY
Currently, the most common technologies for biomass combustion are grate boilers and boilers with fluidized bed boilers. The most suitable boiler technology is always determined for a given application regarding the method of fuel treatment before combustion and its other characteristics (calorific value and heat of combustion, the content of water, minerals, and sulphur in the fuel). Grate boilers and fluidized bed boilers can be generally used for similar applications across various industries. However, grate-firing is well suited for solid fuel combustion. Historically, grate boilers were the most common type of boilers, and even today, modern grate boilers are among the dominant technologies for burning biomass and municipal and industrial waste. For these applications, the typical fuel-feeding systems used in biomass-ﬁred grate boilers are mechanical stokers, which ensure the separation of the sintered layer of fuel, efficient feed and mixing of fuel, and removal of ash from the furnace. Fluidized bed combustion (FBC) boilers utilize the physical process of fluidization, during which granular material is kept suspended by a flow of a fluid medium. The resulting dispersion acts like a liquid in which the fuel particles visually boil, mix freely, and spread over the entire surface of the reactor. In practice, a fluidized bed consists of fuel crushed into small particles through which gas (most often air) flows distributed via a porous layer. The fluidized bed consists of fuel, a desulfurization additive (e.g., limestone), and an additive ensuring the stability of the fluidized bed (inert material such as sand).
Both technologies have specific characteristics, advantages, and disadvantages. FCB excels in quick and effective temperature control and allows for uniform temperature of the mixture, which prevents undesired overheating of the material and ensures low emission values. The disadvantages of FBC technology are the sensitivity to fuel granulometric properties and the risk of agglomeration of fine particles in the fuel bed. The firing of certain fibrous biomass fuels and the use of silica sand for stabilization disrupts the fluidization effect. These problems can be mitigated by the use of special additives or materials. Grate-fired boilers are not subject to these obstacles and are suitable for centralized and decentralized units for combined heat and power generation firing biomass and municipal or industrial waste. Compared to FBC, grate boilers also benefit from lower acquisition costs, easy operation, and simple maintenance. Depending on the fuel type, traveling grates, or vibrating grates are the typically utilized firing systems. Vibrating and traveling grates of PBS Brno are characterized by reliability and long lifetime, enabled by a simple and proven construction of an eccentric drive ensuring the movement and mixing of fuel and ash removal. To ensure maximum economic and environmental benefits, optimal efficiency, and other advantageous operating characteristics, the integration of advanced air and flue gas systems is also necessary. These systems guarantee optimal mixing of air in the furnace, transport of fuel to the furnace space, and balanced coverage of the grate, recirculation, and flue gas cleaning. Modern air and flue gas systems improving the grate boilers efficiency represent the boiler production standard of PBS Brno.
For the heating industry, PBS Brno offers a new product line of hot water boilers of lower outputs for wood biomass combustion for decentralized heating plant operations emphasizing the minimum demands on operation and servicing. Boilers of the PBS BB series are equipped with a control system enabling fully automatic operation. They are designed for burning uncontaminated wood biomass with a maximum humidity of up to 55%, e.g.: wood chips, bark, sawdust, and shavings. The concept of the BB series makes it possible to design a boiler according to the specific requirements of the hot water network, in the range of consumption of 1,2–4,2 t of fuel per hour and a thermal output of 2–7 MW.
PBS Brno standardly supplies modern complex heating units. The main advantage is the achievement of optimal performance, service life, and ecological operation of the entire system by optimizing all subsystems of the energy installation. In addition to the boiler and combustion system itself, the unit consists of devices for the management of fuel, ash, and flue gases, and possibly a tailor-made unit for electricity production. The fuel storage facility and logistic infrastructure ensure a safe and continuous operation. An efficient and constant fuel supply maximizes the energy output and at the same time prevents the excess emission of gaseous and solid pollutants. The operational cleanliness is provided by a high-quality flue gas dedusting system, which filters the flue gases discharged from the boiler into the chimney by a flue gas fan, utilizing an electrostatic precipitator or a cyclone (multicyclone) with a fabric filter. PBS Brno guarantees the fuel consumption corresponding to the projected output, own consumption, flue gas emission parameters, and the acoustic properties of the supplied complex heating units.
The BB series boilers are self-supporting, all-steel design, and water-cooled. The boiler consists of a pressured segment comprising a fireplace with an inclined, sliding, air-cooled grate and a heat exchanger. The boiler is equipped with measuring sensors, inspection holes and manholes. The unit is provided with thermal insulation covered with galvanized or aluminium sheet. The boiler meets the emission limits valid in the Czech Republic (nař. vl. č. 146/2007 Sb.).
Global energy policy focuses on energy efficiency and the increase of renewable energy resources share, whether these steps are prompted by energy security or environmental concerns. The aforementioned implementation of the EU's climate neutrality goal as well as the global reduction of the carbon footprint will require coordinated regulation covering the entire energy system. The goals set are certainly necessary for the environment in terms of future development, but they are certainly very ambitious and pose a challenge from a socio-economic point of view. For this situation, an event from the beginning of this year is quite symptomatic. The European transmission system only narrowly avoided a possible blackout due to the malfunction in the Croatian Ernestinovo substation and the subsequent cascading overload of the neighbouring transmission lines. The experience of Denmark, the pioneer in the share of energy production from renewables, shows that the challenges of energy transformation cannot be solved solely by increasing the capacity of energy production using RES. Therefore, significant changes in regulation and advancements of technologies can be expected, especially in the field of energy storage, which is, especially concerning thermal energy, an accessible and logical direction of development on the path to achieving greater energy efficiency.
Thanks to heat storage capacities, it is possible to transfer energy from a period of relative surplus to a period of relative shortage and thus compensate for consumption peaks accordingly to the achievable operational and economic capacities of the production facility. Also, in the case of combined heat and power generation, support services may be provided, compensating for balancing the electricity system, considering the electricity demand. Heating of the working medium is the most direct and historically first way of heat storage, using specific heat of the substance, optimally with a large heat capacity and a low price, most often water. Dedicated heat storage devices with a massive supporting structure and thermal insulation or heat networks are used for heat storage, which in practice also means the possibility of heat storage from external heat sources.
The primary motivation of the heating industry for developing heat storage capacities is the economic viewpoint. The efficient use of energy leads to lower consumption of primary resources and fuels. Lower pollutant emissions have a positive effect on savings for emission allowances. Also, meeting the conditions of public subsidies can lead to receiving state funding. Another important factor for the establishment of storage capacities is securing a stable supply of heat to customers and eliminating the effects of outages or failures.
Scalable thermal storage systems in particular are an integral part of a viable plan to achieve carbon neutrality. PBS Brno employs a holistic view of energy development and participates in the development and implementation of storage facilities to increase energy efficiency.