APPLICATION OF ECONOMIZER IN BIOMASS BOILER HOUSE I N [615848]

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APPLICATION OF ECONOMIZER IN BIOMASS BOILER HOUSE I N
BORYSPIL AIRPORT: CASE STUDY

Sofiia Heletukha 1, Lead engineer, Master's degree

ABSTRACT

Installation of economizer allows recovering signif icant part of physical and latent heat and reduce
greenhouse gas and dust emissions in flue gases. En ergy and ecology efficiency increment calculations
for the 5 MW biomass boiler house in Boryspil Airpo rt are described in this paper.

1. INTRODUCTION

According to the International Energy Agency, in pr eventing the global temperature
increasing on the Earth more than to 2°C, concernin g to the preindustrial period, the most
important role in reducing CO2 emissions in the per iod up to the 2050 will be playing energy
efficiency (40%) and renewable energy (30%). Energy efficiency in biomass boiler house
concerns both and that's why is actual nowadays.
According to the Energy Strategy of Ukraine until 2 035 [1], Ukraine is going to reduce
fossil fuels consumption and increase the share of renewable energy sources in the total primary
energy production from 4% (in 2016) to 25% (in 2035 ). In recent years, biomass sector has
accounted for about 80% of renewable energy in the country and is based mainly on utilization
of woody biomass in heat generation: wood logs and wood pellets mostly for population and
district heating, wood chips and residues mostly fo r industrial purposes, public heating and
power production [2].
There are different energy loses in biomass boiler houses. Among them: loses due to
chemical and physical incompleteness of combustion, loses by fencing structures etc. But most
of the energy loses in a boiler are because of the high temperature of the flue gas. Boilers
generally can lose 20% of heat of combustion. Thank s to the flue gas condensers boilers can
recover up to 50% of this heat loss [3]. Therefore, recovering the waste heat from flue gas is a
major area to increase the thermal efficiency of pl ants.
Average moisture content of wood chips used in the biomass boiler house is
40-60%. When combustion process starts, the fuel is heated up and water from the fuel starts
to evaporate. Evaporation requires energy and this energy together with wet flue gases is
released in atmosphere and is wasted. Part of this energy can be recovered if wet flue gasses
are directed through a technical device called econ omizer.

2. OBJECTIVES OF THE PROJECT

Municipality owned district heating company supplies district heat for
consumers in Boryspil Airport. Among the heat users there are terminals, public
buildings and commercial buildings. The company own s and operates
three boiler houses. Average efficiency of boiler h ouses is 85%.
In this boiler house there are six boilers with the total installed heat capacity 27 MW: five
natural gas boilers (with total capacity 32 MW) and one biomass boiler POJ INKA 5000 (with
5 MW capacity).
The POJ INKA biomass boiler is operated to cover pe ak loads. The natural gas boilers are
used to cover the base load and as back-up in case of emergency situations.
Economizer type Enerstena CEB 1000 (Figure 1) is in stalled in biomass boiler house.

1Institute of Engineering Thermophysics of NASU, Zhe lyabova 2a street, tel.: +38 044 456 94 62,
e-mail: [anonimizat] ;

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Figure 1: Economizer Enerstena CEB 1000 in biomass boiler house in Boryspil Airport
Flue gases through the inlet pipe are introduced in the condenser. First nozzle circuits are
located in the pipe. In the first step flue gases a re cooled to temperature that is acceptable to
condense heat in the second part. Solid particles i n fuel gases (still left after gas treatment in
the cyclone) are caught in the first nozzle circuit . The previously cooled flue gases are then
injected in the second part of the condenser. Gases are moving from the top to the bottom inside
the pipes and water is injected in intertubular spa ce and moves towards gas. The purpose of the
second step is to perform deep cooling of flue gase s and steam condensing. Consequently the
temperature of water injected through the second no zzles shall be as low as possible. The useful
heat from the condenser is then returned back to di strict heating system.
The objective of this project is to increase the ef ficiency of biomass use by installation of
economizer in biomass boiler house in Boryspil Airp ort.

3. ENERGY EFFICIENCY INCREMENT

The calculations are based on the following initial data:
− type of economizer: Enerstena CEB 1000,
− type of biomass boiler: POJ INKA 5000 (with nominal capacity 5 MWth, actual
capacity is 60% from nominal capacity),
− fuel: wood chips, The moisture content in the fuel is between 40-60% (for further
calculations the moisture content of wood chips wer e assumed 40%);
− return water temperature 40 oC,
− flue gas temperature 100 oC,
− no combustion air humidification is applied.
Heat loss and energy efficiency are calculated for low heating value (LHV) and high
heating value (HHV) for wood-chips-fired boiler POJ -INKA 5000 (Table 1) and system “wood-
chips-fired boiler – economizer” (Table 2).

Table 1: Thermal efficiency of wood-chips-fired boi ler POJ-INKA 5000
LHV HHV Unit
heat
loss with exhaust gas q 2 5,92 20,4 %
with chemical combustion
incompleteness q3 1 0,85 %
with mechanical combustion
incompleteness q4 1,5 1,27 %
with external cooling q 5 0,35 0,3 %
with ash heat q 6 0,1 0,09 %
total heat loss Σq 8,9 22,9 %

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efficiency factor η 91,1 77,1 %
fuel consumption with nominal capacity B 0,537 kg/s 1933,2 kg/h
fuel consumption with actual capacity B р 0,316 kg/s 1137,6 kg/h

Table 2: Thermal efficiency of system “wood-chips-f ired boiler – economizer”
LHV HHV Unit
heat
loss with exhaust gas q 2 -6,25 8,7 %
with chemical combustion
incompleteness q3 1 0,85 %
with mechanical combustion
incompleteness q4 1,5 1,27 %
with external cooling q 5 0,35 0,3 %
with ash heat q 6 0,8 0,68 %
total heat loss Σq -2,6 22,9 %
efficiency factor η 102,6 88,2 %
fuel consumption with nominal capacity B 0,47 kg/s 1692 kg/h
fuel consumption with actual capacity B р 0,28 kg/s 998 kg/h

By establishing a economizer:
 the amount of heat losses with exhaust gas decrease s, which leads to increase of efficiency
of the system. Efficiency factor increased – by 11% , from 77% to 88% (by HHV) and from
91% to 103% (by LHV).
 Fuel savings:
− with nominal capacity – 5000 kW): 241,2 kg/hour;
− with actual capacity – 2944 kW): 129,6 kg/hour;
 with a constant fuel consumption in the system "boi ler-economizer", the amount of useful
heat used in it:
− with nominal capacity – 5000 kW): 5,7 MWth;
− with actual capacity – 2944 kW): 3,35 MWth

4. ECOLOGY EFFICIENCY INCREMENT

The main pollutants formed during the energy use of biomass are nitrogen oxides (NOx),
carbon monoxide (CO), sulfur oxides (SOx), and soli ds calculations are shown in the
Figures 2,3.

Figure 2: NOx, СO, SOx pollutants in wood-chips-fired boiler POJ-IN KA 5000 flue
gases, g/hour
1,674.4 4,081.4
0.0 5000
0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0
Nox СO Sox Pollutants , g/hour
wood chips limit of maximum permissible concentration

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Figure 3: Solids pollutants in wood-chips-fired bo iler POJ-INKA 5000 flue gases in
different variants of cyclone and economizer instal lation, g/hour
Consequently, when burning wood chips in a 5000 kW biomass boiler, emissions of
nitrogen oxides (NOx), carbon monoxide oxides (CO), sulfur oxides (SOx) are acceptable,
and emissions of solids particles:
– without installing of cyclones and an economizer – are higher than the permissible norm:
– with the installation of cyclones, but without th e establishment of the economizer – are
higher than the permissible norm:
– from the installation of the block of cyclones an d the economizer – are permissible.

5. CONCLUSIONS

As a result of above analysis the key conclusions c ould be formulated as follow:
Installation of economizer allows:
− to increase overall efficiency and reducing wood ch ips consumption by 241 kg/hour
(with nominal capacity) and by 129,6 kg/hour (with actual capacity)
− to increase efficiency of the system. Efficiency fa ctor increased – by 11%, from 77% to
88% (by HHV) and from 91% to 103% (by LHV).
When burning wood chips in a 5000 kW biomass boiler emissions of nitrogen oxides
(NOx), carbon monoxide oxides (CO), sulfur oxides ( SOx) are acceptable, and emissions
of solids particles:
− without installing of cyclones and an economizer – are higher than the permissible
norm:
− with the installation of cyclones, but without the establishment of the economizer – are
higher than the permissible norm:
− from the installation of the block of cyclones and the economizer – are permissible.

References
[1] International Energy Agency World Energy Outlook Special Report 2015: Energy an d Climate Change
[2] National Renewable Action Plan till 2020 in for ce since 1 October 2014 (Decree of Cabinet of Minis ters # 902-r)
[3] Geletukha G., Oliynyk E., Zheliezna T. Prospects for heat production from biomass in Ukrai ne – 6th Position Paper
of UABio (in English), Bioenergy Association of Ukr aine, Kyiv, Ukraine, 2013, 22 p.
http://uabio.org/img/files/docs/position-paper-uabi o-6-en.pdf
[4] Kemal Comakli, Meryem Terhan (2016). Energy and Economic Analysis of Heat Recovery from Boiler Exh aust
Flue Gas. International Journal of Energy and Power Engineering: World Academy of Science. pp. 450-456 .
[5] 2. Jakobsen H.H. (1991). Flue Gas Condensation of Chip Fired Boiler at District Heating Plant: Dan ish Institute of
Forest Technology.
293 5,128 14,652
500
02000 4000 6000 8000 10000 12000 14000 16000
with cyclone and
economizer with cyclone without cyclone
and economizer Solids particles, g/hour
wood chips limit of maximum permissible concentration