Cascading of Geothermal Energy in Italy - Geo

This document contains the following article:
Cascading of Geothermal Energy in Italy
From the Geo-Heat Center Quarterly Bulletin Vol. 10, No.1, Summer 1987
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and they constitute the physical and spiritual support on which we all depend upon for survival. At
the same time, people must be allowed reasonable
use of natural resources. Whether we like it or not,
we all live in a world in which environmental planning and management are a necessity. It may take
effort and learning to listen and the art of
compromise-skills which too few of us obviou~-
ly now possess. The consequences of not taking
such care are the eventual loss of our very support
base. The Rotorua bore users controversy contains
a larger lesson for us all.
CASCADING OF GEOTHERMAL
ENERGY IN ITALY
John W. Lund
Oeo-Heat Center
Oregon Institute of Technology
Klamath Falls, OR 97601
Introduction
Monte Amiata, located in central Italy north of
Rome (Figure 1), is an ancient silicic volcanic cone
that still has exploitable geothermal resources.
Since the turn of the century, mercury has been
extracted from Cinnabar, a volcanic deposit in the
region. In the 1970's the international price of mercury fell, sharply curtailing the mining activity. To
find substitute employment for the local workers,
alternative projects were investigated with the use
of geothermal energy the main focus.
A geothermal power plant was constructed iin
1968 near the town of Piancastagnaio on the slopes
of Monte Amiata (Figure 2). This plant, operated
by ENEL, has a maximum capacity of 15 MWe
and operates against an noncondensable gas
pressure (mainly C02). The wellhead output is 198
tonnes/hour of 184 C steam at 9.3 atmospheres.
The gas content is approximately 18070 by weight
of the total output. The plant discharges at 96 C
and 1.04 atmospheres. Four wells, 700 to 1000
meters deep, supply dry steam to the plant. The
recoverable thermal energy is estimated at 75
Gcal/hr (314 GJ/hr), (equivalent to 650 billion
Kcal/yr or 2719 billion KJ/yr - 68,000 tonnes of
oil equivalent).
Figure 2.-Geothermal power plant
ALBANI
A LOW ENTHALPY ZONES
Direct Utilization Project
An obvious solution for employment in the
region was to utilize the waste heat from the power
plant. A greenhouse complex, proposed by INDENI, the responsible government agency, was one
of the best alternatives; however levelland for this
facility was not available near the plant. The
suitable site, approximately 3 km from the plant
and 350 meters lower in elevation, would then require constructing a pipeline and pumping facility.
Since only 20 to 25070 of the available heat from
the power plant would be utilized, the facility was
not economically feasible. This utilization would
occur mainly during the colder late fall, winter, early spring months and at night. To cut economic
losses, an agricultural and agro-industrial byproducts drier was considered. This additional
facility would utilize energy complementary to the
greenhouse use, increasing the overall utilization
to 50 to 60070 of the waste heat, thus making the
overall project economical (Figure 3).
Figure I.-Location of low enthalpy cones in Italy
GHC BULLETIN, SUMMER 1987
13
70
60
_______ ,
50
_0
,,
,,
/
--------
/'
,,
~lilililililil:lil:I:I.I.I:I:lil.I.1
/'
,,
,
,,
,,
,,
30
,----- ----
/'
20
DRIER
10
AUG
SEP
OCT
NOV
DEC
JAN
rEB
MAR
APR
MAY
JUN
JULY
Figure 3.-Geothermal energy consumed by greenhouse and drier
184°C
Turbine/Generator
(15 MWe)
---8
Exhaust
Stack
80°C
Piezometric
Vessel
t
T
97°C
1r-
350 m
Direct
Contact
Condenser
3 km
Future
District
Heating
(Piancastagnaio)
- - - - -..-.l!
~
Storage Tank
(4,000 m3 )
CJB
t
-+
80 C
St orage
Tank
(4,000 m3 (
Greenhouses
(22 hal
and
Future
.
Drying Facilities
Downstream
She ll-and-Tube
Heat Exchangers
Figure 4.-Process diagram of the heat recovery plant and transport system
GHC BULLETIN, SUMMER 1987
14
-----.------.~~
--
Figure 5.-Plate and frame heat exchangers
Figu~e
6.-Shell and tube heat exchangers and
I
pumps
I'
Construction of the Energy Transport System
Construction of the energy transport system
started in 1980. Since the exhaust fluid from the
power plant is high in sulfide and chlorides, it is
highly corrosive. This problem, together with the
large amount of C02, requires heat exchangers to
isolate the fluid. In addition, the large head difference between the power plant and the
greenhouse facility required special engineering
design. The solution was composed of three parts:
I. At the power plant, a primary condensation
circuit made of a direct contact condenser and plate
heat exchangers to isolate the corrosive liquid.
2. A secondary system to transport heat from
the power plant to the greenhouse elevation, starting at the plate heat exchangers and ending in
shell-and-tube heat exchangers. The latter were required by the high pressure from the elevation
difference.
3. A tertiary system at low pressure to transport
heat from the shell-and-tube heat exchangers to the
greenhouse heating systems.
A schematic of the heat transport facility is
shown in Figure 4. Figures 5 and 6 are photographs
of the plate and shell-and-tube heat exchangers,
and circulating pumps.
The primary loop between the power plant and
plate heat exchangers is fiberglass reinforced plastic
pipe that resists the corrosive fluid. Return fluid
at 50 C is sprayed into the direct contact condenser
at the bottom of the 50-meter power plant exhaust
stack and then returned to the plate heat exchan~ers at 90 C. Approximately 2000 tonnes/hour
are circulated in this system.
In the near future, 38 tonnes/hour (1.5 Gcal/hr
or 6.3 GJ/hr of energy) will be removed from this
primary loop and transferred through plate heat
exchangers to heat public buildings in Piancastagnaio. The heat would also be transferred
through plate heat exchangers. Piancastagnaio, an
old walled city, is located just above the power plant
(Figure 7). The town is known as a winter recreation center as skiing is available on Monte Amiata.
Figure 8.-Greenhouses
The plate heat exchangers are designed Ii to
transfer 75 Gcal/hr (314 GJ/hr or 1.13 MWt) to
the secondary loop. This loop, constructed dlf a
buried 65-cm diameter insulated carbon steel pipe,
returns non-corrosive water at 46 C to the plate
heat exchangers and then supplies the water a~; 86
C to the shell-and-tube heat exchangers. The pipe
. J!
ing insulation is polyurethane loam
Wltl\!
a
polyethylene protective layer;
.
The tertiary loop provides 80 C water at a ~,ow
of 2 m/s at 1.0 to 1.5 kg!cm2 pressure to ~he
greenhouses. The water is then returned to the s~fll
and-tube heat exchangers at 40 C. Two 4000-m3
insulated storage tanks are part of the tertiary lobp.
One holds the return water at 40 C and the otrer
holds the supply water at 80 C for peak demand
and backup in case of a temporary system fal'1,1ure.
II
Greenhouse Operation
.
The greenhouses, operated by Floramiata, c~~er
22 hectars with another 11 hectars planned. The
majority have a peaked roof with side wall t~pe
design. Two of these, approximately 50 m by )50
m, are linked, and then connected to a central!;arched corridor approximately 25 meters wide. ~p
proximately 10 of these greenhouses are connec'ted
on either side of the corridor (Figure 8). A for~ed
air system heats the two connected greenhou,ses
through a plastic tube along the center eave (Fig~re
9). Where needed, some have water pipes supPlying heat along the sidewalls and under benches.
Each building has a fossil fuel back-up systJm.
I,
!:
GHC BULLETIN, SUMMER 1987
Figure 9.-Forced air heating system
The majority of the products raised in the
greenhouses are potted plants and flowers. Only
100/0 are cut flowers. The market for these plants
is primarily in Italy, Switzerland and Germany. In
addition to the growing area, the operation has a
research facility. On the average, of the 300 people usually employed, half are retrained miners.
During peak periods, up to 500 are employed.
The greenhouses consume between 130 and 150
billion kcal/yr (544 and 627 billion kJ/yr), while
peak power at night varies between 65 and 70
million kcal/hr (272 and 293 million kJ/hr).
Drying Facility
A drying facility to employ 150 to 160 people
has been planned. It will complement energy use
of the greenhouses by drying local products. Two
basic product lines have been proposed:
I. Feed components for animal husbandry, with
15
an annual production of 100,000 tonnes of dried
products.
2. Dried vegetables for human consumption, at
an annual production rate of 3,500 tons.
The total annual consumption of energy for
these lines is estimated between 200 and 220 billion
k/cal (836 and 920 billion kJ).
Operation and Economics
The heat supply system to the greenhouses is
operated and supervised from the control room at
the power plant. These pipe lines and heat exchangers are equipped with a safety system that
compares upstream and downstream flow rates,
and thus detects leaks. In the event of a leak, the
pumps can be stopped and valves closed on the
pipeline. The system is also self-regulatory and adjusts automatically to changes in heat load by the
user.
The construction and operation of the facility
is a joint venture between ENEL and INDENl.
ENEL will not charge for exploration and drilling expenses. They will only charge INDENI and
the users, a consortium of the Amiata communities, a fee for twenty years to cover return on
invested capital, relevant interest and operating
costs of the recovery, transport and distribution
plant. The greenhouse company will pay 40010 of
the total annual fee and the drier company will pay
the remaining 60%. The estimated gross profit is
9% for the greenhouses and 11 % for the proposed drying facility. Using fossil fuel for energy,
neither process would be profitable, but the low
profits are justified by employing the local
population.
The Monte Amiata project is a good example
of a cascaded use of geothermal energy, and brings
together two public energy authorities to solve a
local economic and social problem.
Acknowledgement
I would like to thank the personnel of ENEL,
INDENI and Floramiata for answering questions
concerning this project during the field trip of the
UNITAR/UNDP Workshop on Small Geothermal
Resources, May 1987, Thanks also to Dr. Joan
Foster for assisting in the editing.
References
I. Francia, c., E Calcara and G. Mariani, 1982.
"Multipurpose Utilization of Geothermal Energy:
INDENI - ENEL Geothermal Project on the
Amiata;' Proceedings of the International Conference on Geothermal Energy, Florence, Italy
(BHRA Fluid Engineering, England), pp. 43-54.
(May)
2. Costantino, E, and A. Palama, 1982. "Design
of an Atmospheric Condenser for Direct Use of
Geothermal Steam Condensates;' Proceedings of
the International Conference on Geothermal
Energy, Florence, Italy (BHRA Fluid Engineering,
England), pp. 55-61. (May)
THE ABSORPTION POWER
GENERATOR
Charles T. Sundquist, P.E.
1971 Sheridan Place
Richland, WA 99352
*Editor's Note: Mr. Sundquist's patent, described in this article, may have
application in the fields of geothermal power generation. He is seeking support for its commercial development. The Geo-Heat Center neither endorses
nor disclaims the invention.
The absorption power generator is an apparatus
for generating power from low temperature heat.
It is a recent invention, protected by U.S. Pat
#4,662,820. It has possible application in the fields
of geothermal power generation, waste heat utilization, and cogeneration. A flow diagram of the apparatus is shown in Figure I. The basic components
are an evaporator with vertical heating tubes, a
prime mover, an absorber, a solution pump, a solution heater, a condenser, a condensate pump, a condensate cooler, and a heat exchanger. A vaporous
fluid, like ammonia, and an absorbent liquid, like
water, are used in the process. The flow of high
pressure vapor, generated in the evaporator, is divided into two parts. One part is expanded in the
prime mover. The low pressure vapor, coming off
the prime mover, is then absorbed in a spray of
absorbent liquid in the absorber. The other part
of the high pressure vapor flow is condensed in a
high pressure condenser where the temperature is
held above that of the available cooling medium.
A critical component of the invention is the
evaporator with its vertical heating tubes. Heated
strong solution flows downward very slowly inside
16
the vertical heating tubes, undergoing a large
temperature drop. At the bottom of tubes, the
strong solution mixes into weak solution in the shell
space of the evaporator. Weak solution, from the
bottom of the evaporator, is then sprayed into the
absorber and absorbs the low pressure vapor coming from the prime mover. Heat, transferring
through the vertical heating tube walls, is
transported upward through the weak solution and
into the high pressure vapor. A spray of condensate, in the vapor space of the evaporator, rectifies
the vapor coming from the boiling surface of the
weak solution. Rectification of the evaporator
vapor accomplishes two purposes. One is to hold
down the temperature of the high pressure vapor
and, in turn, the required temperature of the strong
solution leaving the solution heater. The other is
to increase the ratio of the flow of weak solution,
entering the absorber, to the flow of low pressure
vapor, entering the absorber. This increases the
pressure drop at the prime mover and thus provides more power from each pound of high
pressure vapor.
The heat of absorption, recovered in the ab-
,sorber, is recycled back to the evaporator where it
is reused in the evaporation process. Likewise, some
of the heat of condensation, from the condenser,
is recovered in the heat exchanger and is recycled
back to the evaporator. Using ammonia and water,
a net possible thermal efficiency of approximately 14% is estimated. The vapor pressure in the
evaporator would be 210 psia. The temperature of
the heating fluid supplied to the solution heater
would be 150F. The maximum air temperature,
entering the condensate cooler as in Figure 1, would
be 90F.
Figure 1.
GHC BULLETIN, SUMMER 1987

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