A geothermal development project has been initiated at the Lawrence Livermore Laboratory (LLL) to emphasize development of methods for recovery and conversion of the energy in geothermal deposits of hot brines. Temperatures of these waters vary from 150 C to more than 300 C with dissolved solids content ranging from less than 0.1% to over 25% by weight. Of particular interest are the deposits of high-temperature/high-salinity brines, as well as less saline brines, known to occur in the Salton Trough of California. Development of this resource will depend on resolution of the technical problems of brine handling, scale and precipitation control, and corrosion/erosion resistant systems for efficient conversion of thermal to electrical energy. Research experience to date has shown these problems to be severe. Hence, the LLL program emphasizes development of an entirely different approach called the Total Flow concept

Austin, A. L.

English

NASA Technical Reports Server

THETOTALFLOWCONCEPTFORGEOTHERMAL 
ENERGY CONVERSION 
A. L. Austin 
Lawrence Livermore Laboratory 
University of California 
Livermore,  California 
A geothermal development project has been initiated at the 
Lawrence Livermore Laboratory (LLL) to emphasize develop- 
ment of methods for recovery and conversion of the energy in 
geothermal deposits of hot brines. Temperatures of these waters 
vary from 150°C to more than 300°C with dissolved solids content 
ranging from less  than 0.1% to over 25% by weight. Of particular 
interest a r e  the deposits of high-temperature/high-salinity brines, 
a s  well as less  saline brines, known to occur in the Salton Trough 
of California. Development of this resource will depend on reso- 
lution of the technical problems of brine handling, scale and 
precipitation control, and corrosion/erosion resistant systems - 
for efficient conversion of thermal to electrical energy. Research 
experience to date has shown these problems to be severe. Hence, 
the LLL program emphasizes development of a n  entirely different 
approach called the Total Flow concept. This, in principle, con- 
sists of passing the total hot wellhead brine-steam mixture directly 
through a mixed-phase expander to drive an  electrical alternator. 
The purpose of this paper is to define the basic thermodynamics 
of this concept, expander requirements, and overall system 
characteristics. 
Total Flow System will be discussed along with comments on 
current laboratory and field activities. 
The LLL program plans for development of a 
It is  generally accepted that the water-dominated geothermal resources, 
if developed, could produce a significant supply of clean, low-cost energy. 
Temperatures of these waters vary f rom 150°C to over 300°C with dissolved 
solids content ranging f rom l e s s  than 0. 1% to over 25% by weight. 
Of particular interest a r e  the deposits known to exist in the Salton Trough 
of California. 
about 60,000 to over 10 million megawatt-years. 
due to lack of data on the magnitude and distribution of the stored thermal 
energy, and to uncertainties regarding technological prospects for economic 
recovery and conversion of the energy from the high saline waters. The cur- 
rent interest in conversion machines and systems designed uniquely for these 
resources is  stimulated mainly because hot water resources a r e  abundant, 
economic conditions encourage development of machines with highest efficien- 
cies to minimize the number of wells per  unit of electrical output, and the 
Estimates of the recoverable energy from this region range from 
This variation is primarily 
186 
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range’of chemical conditions encountered may require development of special 
systems, each tailored to specific resources and locations, 
Development of .the high saline waters, in particular, will depend on 
resolution of the technical problems of brine management, scale and precipi- 
tation control, and corrosion/erosion resistant systems for efficient, economic 
energy conversion systems. Solution of these problems coupled with a need 
to better understand the mechanisms governing reservoir lifetimes and pro- 
ductive capacities will require a broad interdisciplinary approach. 
Before a commitment to commercial production can be made, a goal 
oriented research and development program is required to reduce the tech- 
nological r isks to an acceptable level. To accomplish this, a geothermal 
development program has been initiated by the AEC a t  the Lawrence Livermore 
Laboratory (LLL) to emphasize development of methods for  recovery and 
conversion of the energy in the high temperature/high salinity brines. 
experience to date on systems operating from these brines has shown the prob- 
lems to be severe. Hence, the LLL program emphasizes an entirely different 
approach called the Total Flow Concept for energy conversion. This, in 
principle, consists of passing the total hot wellhead brine-steam mixture 
directly through a mixed phase expander to drive an electrical generator. Fig- 
u re  1 shows a comparison of this process with the Flashed Steam System on the 
Temperature-Entropy plane. 
of the wellhead product f rom state point 1 to the exhaust pressure at 2. 
i s  thermodynamically the simplest, and provides an upper bound on cycle 
efficiency. Regardless of the number of separation stages used in the Flashed 
Steam System, there will always be some useful energy discarded with the 
separated brine, e.  g. , the path A-B. 
Research 
The Total Flow process involves the expansion 
This 
A detailed analysis of these systems operating from brines of different 
temperatures has been completed. 
60% increase in power output can be achieved with the Total Flow System if it 
can be made to function with a 7070 engine, o r  expander, efficiency. 
increase, of course, translates directly into a corresponding decrease in the 
number of required production wells and a reduction in capital investment. 
The results (Figure 2) show that about a 
This 
In order to gain this advantage, however, it is  necessary to extract the 
maximum available energy from the wellhead product. 
basic problem. For  the particular case shown (p i  = 360 psia, x i  = 19%, and 
expansion to 3.5-inch Hg (120°F) condenser pressure)  which is typical of high 
temperature geothermal wells, it is shown that 2/3 of the available energy is 
obtained by expansion from about 50 psia down to the sink condition. Hence, 
any Total Flow System expander must  be capable of economic operation over 
the entire pressure range in order to produce the performance depicted in 
Figure 2. This means that expanders with limited expansion ratios (such as 
positive displacement devices) must be multiply staged to recover the available 
energy. Since the fluid specific volumes, for the example shown, increase 
from about 0 . 3  ft3/lb. to about 70 ft3/lb., the physical size of the low pressure 
stages of positive displacement devices increase accordingly, leading to enor- 
mous machines, and possibly, high costs. Consequently, development of single 
stage expansion devices and/or hybrid systems will likely be necessary to gain 
the full benefit of the Total Flow process. 
for example, may consist of a Total Flow device as a topping stage with exhaust 
to a Flashed Steam System. 
187 
Figure 3 illustrates the 
. For some applications the latter,  
I 
Development of any conversion system for use with a high saline brine is 
complicated by the presence of a s  much as  26% dissolved solids. Precipitation 
of silica and other solids can cause rapid formation of scale on components and 
outlet piping, Consequently, a system must be designed to either allow contin- 
uous removal of scale, o r  precipitation and deposition control during operation. 
Coupled with this a r e  problems of corrosion and erosion of materials. While 
materials technology advances have produced possible solutions, field exper- 
ience is lacking. Field testing of candidate materials in actual brines under 
operating conditions must precede final system design. Hence, a complete 
system approach to development of the Total Flow concept is necessary, and 
must involve elements of earth sciences, brine chemistry, materials tech- 
nology, conversion and sys tem engineering. 
The LLL geothermal program is directed toward applying and extending 
these technologies where necessary with emphasis on development of the 
Total Flow concept for recovery and conversion of the energy in t h e  high saline 
brines. 
Initially, the major program emphasis will be on solutions of the brine chemistry 
problems and development and testing of expander concepts f o r  energy. 
The key technical issues to be resolved a r e  illustrated in Table 1. 
Because of the advantages of full expansion of the wellhead product a s  
shown by Figure 3,  i t  appears that the impulse turbine may emerge as  the prime 
candidate. It is  simple, contains one moving part, the technology is already 
well known, and offers design flexibility. Most importantly, designs utilizing 
tangential, radial, o r  axial flow can be used to accommodate a wide range of 
operating conditions. These machines can be designed to be sufficiently com- 
pact to accommodate complete wellhead fluid expansion. 
The important feature of the impulse turbine is that the expansion takes 
The momentum of these jets is  then 
place in a converging-diverging nozzle to convert fluid enthalpy to kinetic 
energy in the form of high velocity jets. 
transferred to the impulse wheel which operates a t  the condenser temperature. 
Hence, the entire pressure drop takes place in a single component, fixed in 
space, which offers opportunities for  scale control and brine treatment by tech- 
niques such as  keeping the nozzle walls hot, periodic flexing, chemical treat-  
ment, boundary layer control, etc. One concept, among others, under 
development is shown in Figure 4, which illustrates a tangential flow device 
currently being designed for test. 
It is  well recognized that the major technical problems with such devices 
a r e  the design of efficient nozzles and development of turbine blading to accom- 
modate the mixed-phase flow. 
indicate, thus far, that efficient transfer of the momentum of the liquid phase 
is one of the major design tasks. 
ent in these early calculations limit their value as a precise design tool. 
the development of efficient two-phase conversion machinery will require 
emphasis on experimental techniques. 
Analytical investigations a r e  in progress and 
However, the simplifying assumptions inher- 
Hence, 
A geothermal test facility has been constructed at LLL for  performance 
testing of candidate turbines, and to provide a means of test and development of 
turbine components such a s  nozzles and blading. This facility consists of a 
188 
boiler capable of producing about 1.5 lb / sec  of water a t  1000 psia and 550°F. 
By flashing, a wide range of typical wellhead thermodynamic characteristics 
can be reproduced. 
ation a t  backpressures down to about 3.  5 inch Hg (120°F). 
exists for  complete testing and evaluation of Total Flow machines up to about 
100 kW in capacity as  well as  the means f o r  fundamental investigation of the 
mechanics of two-phase flow. 
which shows a cutaway of the test  chambers and control room. 
The facility includes condensing equipment to allow oper- 
The capability now 
The system is shown schematically in Figure 5 
In conjunction with this, field testing on a high saline well in the Imperial 
Valley has begun. 
and over-simulated turbine blades for preliminary material screening and 
early evaluation of brine handling and scaling problems, 
be adequately simulated in the laboratory under dynamic flowing conditions, i t  
i s  necessary to car ry  out brine analyses and treatment experiments in the field, 
on a flowing well. Preliminary results indicate that one material (Teflon PPA)  
underwent l O O  hours of tes t  without significant scaling in the nozzle o r  erosion 
of the wear plate. Additional tests of other materials a r e  being prepared, and 
field systems for instrumentation and brine analysis are being designed for 
use this fiscal year. 
This currently is  limited to flowing brine through nozzles 
Since the brines cannot 
The overall LLL program goal is the development of complete Total Flow 
systems for recovery and conversion of the energy in hot water deposits with 
emphasis on the high salinity resource. 
is  planned for  early F Y  77. Laboratory and field testing of small scale brine 
tolerant turbines is  scheduled for completion by the end of F Y  76.  Culmination 
of this development effort should lead to a baseline design for a brine tolerant 
Total Flow conversion system which will include evaluation of commercial con- 
figurations a s  well as  specially designed units. During this time, plans for site 
selection and development (including drilling) will be made so that construction 
of a complete demonstration system of about 10 MW capacity can be initiated 
in P Y  77.  Depending on the results of the research efforts, installation and 
operation of the 10-MW experimental power plant is  planned for F Y  79. 
Resolution of the key technical issues 
This experimental plant is intended to contain all  the necessary elements, 
including methods for control, fluid handling, reinjection, condensing and cool- 
ing, and fully instrumented for determining operation characteristics. 
intended that the system be experimental in nature in order to provide a flexible 
test  facility for evaluation of candidate energy conversion systems 
involvement of private industries with machines, techniques, o r  systems for  
application to the Total Flow process will be actively sought. Current involve- 
ment consists of coordination with those doing similar development work, 
development of agreements to gain access to Rowing wells, and negotiations for 
purchase of existing conversion machines for  test  and evaluation on the LLL 
tes t  facility prior to field testing with high saline brines. 
It i s  
Early 
189 
Table I.. High-temperature high-salinity geothermal program 
key technical issues 
C onve r s ion Chemistry and Resource 
materials characterization 
Total flow concepts Brine chemistry Location and magnitude 
Develop baseline 
design 
Scaling mechanism Geochemistry 
Component tests Precipitation Reservoir lifetime 
Small-scale turbine 
Productive capacity 
System design and Material selection 
optimization 
Contr ol . Corrosion 
Condensing and disposal Erosion 
Hybrid systems Fabric at ion 
Plant characterization 
E c onomi c s 
190 
T T 
Fig. 1. Comparison of flashed steam and total flow systems 
12 
10 
- 
e 
I 
s 6  3 a 
8 4  
i 
9. 
f 
c 
2 
Friction factor = .W 
Wellbore area = 2 5  f? 
Self pumping mode 
300 400 500 600 
Reservoir temperature - "F 
Fig. 2. Comparison of geothermal power systems 
191 
Fig. 3 .  Recovery of available power for an  isentropic expansion 
of wet steam characteristic of a hot-water geothermal well 
nozzle steam +water 
from geothermal 
well 
v 
t 
Fig. 4. Tangential flow experimental turbine for total flow 
geothermal application 
192 
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The total flow concept for geothermal energy conversion

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