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Fuel and Energy Complex in the context of Energy Security of Ukraine. Innovative Solutions based on the Steam-Niche Technology of Fuel Combustion

  Ő.Z.Abdulin, Deputy Head of CITNPP Department at NTUU "KPI"

    At present time, natural gas is the most promising and ecologically clean fuel in the world, which causes an increase in number of its customers and volume of extraction and simultaneous expanding range of sources (coal mine methane, syngas, etc.).

    In Ukraine, the specific consumption of natural gas in fire engineering (FE) equipment is much higher than in the industrialized countries. At the same time, the price increase for imported natural gas negatively affects the stability and well-being of the population of Ukraine, which is the result for higher utility costs and products prices of Ukrainian enterprises. Now, there are general trends for the transition to alternative gas fuel in Ukraine. However, there is still a lot of gas-fired equipment, which can not be immediately abandoned and it requires energy-efficient technologies for gas burning only. It explains the urgency of the problem for savings and sustainable use of natural gas and the necessity for immediate reconstruction of the various sectors of the national economy.

    Today in post-Soviet countries, hundreds of thousands of fire engineering units, the service life of which exceeds 20 years, are being operated. Outlast of the designed service life and the current situation of gas delivery (pressure drop in pipelines, pressure pulsation, variation in calorific characteristics of gas etc.) form the present situation and particularity in operation of the facilities. 

    Trouble-free, efficient and environmentally friendly operation of the equipment is possible only when the requirements of modern high-quantitative and qualitative characteristics for the furnance process of the fire engineering facility (FEF) are kept. 

Therefore, the main requirements are the following:

  • uniformity of furnace temperature field providing appropriate heat absorption by furnace tubes, thus, reducing the possibility of local overheating and burnout of heating surfaces;

  • uniformity of heat input in the combustion space in a wide range of loads. This requirement is conditioned by the need of the continuous running boiler operation with significantly lower nominal loads preserved at nominal or even more basic level of thermal performance indicators;

     

  • minor hydraulic resistance in fuel and oxidant paths. Meeting the requirement makes it possible to improve the boiler efficiency significantly at low loads via complete shut-down of the draft system and allows operation of fire engineering facility at minimal gas pressure parameter: 1-5 mmWC.

    Currently in Ukraine, there is a large number of different types of burner devices (BD) from leading global producers. While developing the devices, they try to ensure the feasible distribution of fuel in the oxidizer flotation, the agitation of the fuel mixture and recirculation of mixing zones in the flame stabilization zones. However, it is possible only in a very narrow variation range of operational factors; therefore, the fulfillment of the set requirements to the burner process is not provided to the fullest extent.

    Multi-year researches in main stages of the BD workflow were carried out in the Laboratory of Combustion at NTU "KPI" and revealed the crucial role of the aerodynamic processes that allows to classify the BD types of two gas-dynamic schemes for fuel and oxidant delivery.

    BD operation is complicated in variable modes by destruction of circulation zones of overheated combustion products that provide aerodynamic stabilizing of combustion through violation of uniform distribution of fuel in a oxidizer flotation and fuel mixture output concentration in the recirculation mixing zones beyond of the ignition.

    In order to solve these issues, it is necessary to apply fuel combustion technologies, which are based on the gas-dynamic scheme that involves a cross flow of fuel from the oxidizer flotation before the vortex-creators as niches (stream-niche system).

    Within stream and niche system, in a wide change range of operation factors (gas and air speed, pressure, temperature), stable and maneuverable vortex structures are realized with high-intensity turbulence of fuel and oxidant flotation; and recirculating mixing zones provide high-quality mixing with the required level of fuel concentration and reliable aerodynamic stabilization of the combustion. The volume of vortex is incomparably smaller than conventional eddy BD, therefore, their impact on the boiler furnace pulsation and erosive effect on the embrasure and other elements of the boiler is relatively small. The small volume of vortices allows a start-up and operation of BD with low gas consumption that secures start-up. Improvement of BD mixing properties increases the level of operational reliability at extremely low excess air ratios and, therefore, at higher values of the average flame temperature in the furnace.

    All the above advantages of the stream-niche system allow increasing of the heat absorption of radiant surface and lead to lowering the temperature of stack gases, because the transmitted radiation heat in the furnace is proportional to the flame temperature to the fourth power. Increase of the average level of temperature uniformity in the boiler furnace, that is a result of optimal mixing, is accompanied by a significant decrease in the variation of heat flow, thus increases the reliability of the boiler as a whole. Ordered structure of fuel and oxidizer in BD with the stream-niche system provides self-cooling of the BD elements by means of heat exchange processes during the heating of air and gas. One of the peculiarities of the stream-niche system is a small hydraulic resistance Óf fuel and oxidizer paths, which can significantly reduce the pressure of gas and air in BD operation. All these facts allow the combustion technology optimally fit into the complex scheme of the aerothermochemical fire engineering facility.

    The devices, that implement the stream-niche technology of fuel combustion (SNT), are widely applied at public utilities, construction, chemical, coal, confectionery, food and other industries of Ukraine, Belarus and Russia.

    SNT not only operates on the new equipment, but also allows to upgrade in short-term the outmoded fire engineering facilities (with service life over 30 years) and provide specifications with the global best parameters of efficiency, environmental safety and reliability.

    The payback period of such modernization does not exceed a year of operation only at the expense of fuel savings. There is a list of other advantages: significant energy savings, increased turnaround time of facilities, security enhance, etc.  Currently, 192 multi-operated models of SNB, SNT and VRAD SNT burner devices are certified.

    Many years of operation of fire engineering facilities demonstrated that innovative solutions in the field of energy saving based on the stream-niche technology of fuel combustion provide the most efficient use of energy.