LOW POWER COGENERATION INSTALLATION USING SOLID VINEYARD WASTE BIOMASS Ion Oprea 1 University POLITEHNICA of Bucharest ABSTRACT Our country owns… [615837]

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LOW POWER COGENERATION INSTALLATION
USING SOLID VINEYARD WASTE BIOMASS

Ion Oprea 1
University POLITEHNICA of Bucharest

ABSTRACT

Our country owns important vineyard cultivated sur faces. Along with other forms of biomass,
vineyards have the necessary energy characteristics to be used as renewable fuel in electrical / therm al
energy producing in small power plants. This paper aims to demonstrate the viability of a low power
cogeneration power plant when using such a resource .

1. INTRODUCTION

The use of biomass for energy production is an impo rtant way to reduce the impact of
energy systems on the environment and to implement the rules brought in this field by
European Union. Although the biomass has a consider able share in renewable energy in our
country, it has a reduced use for the production of electricity and heat, whether centralized or
collective-decentralized. The installed production capacity was 130.4 MW on April 1, 2018,
and prospects for the next three years are given in Table 1 [2].

Table 1. The evolution of net power available for b iomass [MW]
2018 2019 2020
150 160 180

Biomass is commonly used in rural areas for heatin g and for food preparation. We
generally talk about low efficiency and high emissi on installations. About 14% of the biomass
energy is generated in modern facilities.
The paper considers the solid biomass from the vin eyards that is the grapevines obtained
from the autumn and spring cuttings. Vines can be u sed energetically after drying, either by
chopping them or as pellets.

2. VINE ROOTS – RENEWABLE ENERGY FUEL

Vines are obtained from the maintenance process of the vineyards, from the autumn and
spring cuttings. Together with grape stones, the vi nes represent the renewable energy source
of wine cultures. The area planted with vines was a pproximately constant in recent years,
being 177.150 ha in 2017 [4, 5] and providing a saf e source of raw material. However, in our
country we cannot speak of a tradition in energy re covery of vineyard byproducts. This is due
to the wide spread of crops, the lack of harvesting and baling machines, and the lack of drying
and storage infrastructure. In this context, the en ergy recovery of vineyards must also take
into account solutions that allow combustion togeth er with wood waste, agricultural biomass
and biomass from energy crops (energy willow, popla r etc.) in the form of pellets, briquettes
or chopped.

1 Splaiul Independentei nr. 313, sector 6, Bucharest , ROMANIA, PC RO-060042 , +4021 4029158, [anonimizat]

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In order to be handled, stored and processed, the v ines are harvested and packed with a
special machine (Fig. 1). The typical dimensions of a bale are: diameter = 40 cm / length = 60
cm and weight of 15 kg/bale being easy to handle. D uring storage, the vines are dried, and
when the humidity drops below 20 percent, bales can be cut or milled to serve as fuel in
heating systems, or can be made into pellets. Upon cutting the vines have an average relative
humidity of 35% and the lower calorific value is Q iw ≈ 12400 kJ/kg and, after drying, at 10%
humidity Q i ≈ 16560 kJ/kg [9, 16]. By storage and drying, the vin eyards reach an average
moisture content of 10%, optimal for storage, burni ng or gasification, with a lower average
calorific value Q i ≈ 19000 kJ/kg; the price is about 0.50 RON/kg.
One hectare of vineyard cultivation has an average of 4000-5000 vine stocks that
produce (0.5-1) kg of biomass/vine stock with relat ive humidity in the range of 30% to 40%,
so between (2000-5000) kg/ha.year [9, 14]. These va lues can vary widely depending on
variety, soil and climatic conditions. Estimating m inimum mass of cut vines of about 2000
kg/ha, it follows that the minimum annual energy po tential of one hectare is E pcv = 24.8
GJ/ha.year.
At national level, taking into account an area of a t least 100,000 hectares of vineyards
in production, the energy potential in the biomass from vines is E pcv ≈ 2480 TJ/year, which
corresponds to an annual consumption of 43,000 tons of diesel and to reducing CO 2 emissions
by 128,000 t CO2 /year which are appealing results.

3. LOW POWER COGENERATION INSTALLATION

The energy recovery of grapevines or mixtures of g rapevines and logs can be done by
using chopped material or pellets in low-power coge neration systems with a back-pressure
turbine or in ORC installations using organic fluid cycles.
Back-pressure turbines best meet the requirements of low-power cogeneration plants
through efficiency, gauge and simplicity of the the rmal circuit. The major disadvantage of
back-pressure turbines is the dependence of their o peration on the heat consumer. In the
absence of the heat consumer, the turbine must be s witched off or provided with a reduced
cooling bypass system. Low thermal loads also reduc e the plant's efficiency.
ORC installations using organic fluid cycles typica lly consist of two main modules:
– a module that ensures the burning of solid biomas s and generates heat;
– a module that produces electrical and thermal ene rgy in which the working fluid is organic.
The interface between the two modules is a heat ex changer. Such an installation can be
used for both residential and small-scale heating. Power generation is achieved with a turbine
that can be axial or radial-centripetal.
The proposed cogeneration plant recovers the energ y potential of vines as such or in
blends with waste / wood waste. This plant is desig ned for local heat supply of residential or
small-scale enterprises. At the same time, the plan t produces electricity to be injected into the
national grid. The plant is destined for the Vrance a region, an important wine region with an
area planted with vineyards of about 17,000 ha [4].
The construction type of the installation has been chosen taking into account the
following main elements:
– the required heat load – a low-power plant was chos en to locally recover the energy
potential of the vine. The potential heat consumer may be a woodworking or an agricultural
products processing enterprise to which hot water i s supplied. If an outlet pressure reduction
and cooling station is provided, it could also feed residential consumers. For industrial
consumers, the outlet pressure is 6 bar. In the cas e of a residential complex for the summer
period, the heat consumption will be significantly reduced, which will affect the performance
of the plant, and the outlet pressure will be 1.2 b ar. We chose the 6 bar outlet pressure, while

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the electrical and thermal loads are to be determin ed by system calculation according to the
available heat provided by the burning of the vines .
– combustion mode of biomass – In principle, two type s of boilers can be selected: with
grate burning or with burning in suspension. Instal lations and studies show that grate burning
allows for higher thermal and electric loads of abo ut 2 MWt and 250 kWe, while the burning
in suspension required a 1.2 MWt and 140 kWe boiler s. The way of preparing the biomass
differs depending on the two solutions, namely on t he grate it is burned in the form of pieces,
pellets or briquettes, while in suspension it is bu rned as splinters or powder. Vines can be
prepared for both combustion modes. For the solutio n calculated, we selected a boiler with a
burning suspension of chopped vines alone or mixed with chopped wood. Boiler parameters
for steam produced are in the ranges p o = (20 ÷ 60) bar; t o = (250 ÷ 450) oC. We opted for live
steam parameters p o = 30 bar; t o = 300 ° C
– type of energy machine – you can choose between a steam turbine or an organic fluid
turbine if you opt for an installation that also in tegrates an ORC cycle.
Due to the fact that the plant is low power, accord ing to the live steam parameters adopted,
the steam flow will be reduced, although the specif ic volume is relatively high, which can
cause problems with the intake section. Adopting a high speed may partially offset this
shortcoming, but it is necessary to use a gear box to drive the electric generator. The steam
turbine can be axial type with one or more stages, or axial radial type recommended for small
enthalpy drops. In this situation we have chosen ax ial radial type a speed of 9000 rpm.
– a simpler heating circuit, which reduces the cost o f the plant and is easy to operate.
Choosing a back-pressure turbine simplifies the the rmal circuit compared to a condensing
turbine. We have opted for the lack of preheating o f the supply water; in the heating circuit,
only a pressure degasser is provided, 6 bar, which is supplied from the turbine exit orfrom the
live steam by means of a pressure reduction; the su pply water temperature will
correspondingly be about 160 oC. For the safety of the heat supply to the heat co nsumer, there
is also a cooling reduction device in the circuit t hat bypasses the turbine.

4. PRELIMINARY CALCULATIONS

The following input data is considered:
– the amount of available biomass – given that, prese ntly, the energetic recovery of the vine
rows is happening randomly in very low power plants , we considered the harvesting of the
vines on an area of about 15% of the potential of t he Vrancea region, 2550 ha respectively.
For a vine waste production of 3000 kg/ha.year, the annual quantity will be 7650 t/year.
Under these conditions, the amount of heat availabl e for an annual heat supply of 8400 hours /
year and a calorific value of 12400 kJ/kg of vineya rds is 93744 GJ/year
– the characteristic parameters of the thermal cycl e are:
• estimated boiler efficiency ηcaz = 0,80
• live steam parameters p o = 30 bar, to = 300 oC
• turbine outlet pressure p e = 6 bar
• water supply temperature t aa = 160 oC
• water supply pressure p aa = 36 bar
– the steam flow rate corresponding to these paramete rs is 1.083 kg/s.
The installed electric power is 0.179 MWe and the thermal power is 2.326 MWt.
The cogeneration plant is expected to operate 8400 hours per year, producing heat and
electricity at nominal capacity. The winter operati ng time is 4400 hours/year, summer 4000
hours/year. Annually, 1504 MWh/year and 19538 MWt w ill be produced.
The value of the investment is estimated to be 3,7 50,000 RON and includes a solid
biomass boiler, a back-pressure turbine (fully equi pped), degasser, heat exchangers, pumps

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(condensation, water supply, district heating), aux iliary (control, pipelines, fittings), bunker
storage, civil buildings, facilities, personal trai ning
The economic analysis period is 10 years. The purc hase price of the vines waste is 500
RON/ton, the selling price of electric power is 150 RON/MWe, and the selling price of
thermal energy is a variable that dictates the prof itability of the project; a value of
250 RON/MWht was chosen; the return rate of investm ent r = 10%.

5. RESULTS AND CONCLUSIONS

The solid waste of vineyard can be used in combine d heat and power small power plants,
responding to the strategy of distributed energy pr oduction, with economical and social
benefits of local community.
The economic performances of the analyzed cogenera tion plant show the viability of the
solution. The net present value is 1,211,177 RON; t he internal rate or return is 15.71 %, the
investment is recovered in 6.5 years and the ratio benefit/cost is 1.33.
Acknowledgments
This work was supported by a grant of the Romanian Ministery of Research and Innovation,
CCCDI – UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0404 / 31PCCDI/2018 ,
and project number 37BMPNIII-P3-199/2016-I05.16. 01, within PNCDI III

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