Mapua University

School of Mechanical and Manufacturing Engineering

Application of Fluid Machinery:

GEOTHERMAL PIPING DESIGN

By

Federis, Joshua Phillip A.

A Technical Paper submitted to the

FLUID MACHINERY
ME143-2 / C1

Engr. Jennifer Buenconsejo-Valdez

Mapua University
October 2020
 NOTA BENE

The author does not claim ownership of all the pictures and diagrams used in this paper.

To check the sources and references to all the statements presented in this paper, proceed to the

last page of this paper to see the References section.

ABSTRACT

The study of fluid machineries imposes great importance as it have a direct use and

application in the real world. One of the primary applications of studying fluid machinery is its

use in pipe designing and pump selection. Pipe networks are integral part of how society operate,

from the waterline networks that supply water to urban housing and industrial plants, to the

HVAC systems that ventilate shopping malls and manufacturing plants. These networks are

comprised of elements such as pipes, pumps, valves, blowers, fans, and compressors etc. But

these elements cannot just be used randomly, careful design and selection of elements are

necessary. One of the industries that exploit this greatly is in the Geothermal Powerplant

construction, because of how they extract their main source of energy to be converted to
electrical power. Pipes are driven on the ground to the natural steam reservoirs which are then

pumped up to the surface to be processed.

1. INTRODUCTION

Pipe networks are integral part of how society operate, from the waterline

networks that supply water to urban housing and industrial plants, to the HVAC systems that

ventilate shopping malls and manufacturing plants. These networks are comprised of

elements such as pipes, pumps, valves, blowers, fans, and compressors etc. But these

elements cannot just be used randomly, careful design and selection of elements are

necessary. According to Miranda & Lopez (2011), piping design is done to transport fluid

safely and economically from one point to the other in consideration of the pressure losses.

Main elements that are being considered in piping design are the pipes and pumps to be used.

2. PIPE SYSTEM

Pipes are tubes that are used to carry and transport fluids and relatively fitting

solids. In piping system, pipes are not just one being considered, it includes pipe fittings such

as valves, elbows, and flanges. Moreover, pumps and heat exchangers are machineries that

are considered as well.

2.1. Piping Material

Correct materials to be used for the manufacturing of pipes must be chosen based in the

operating conditions of the piping system. Similarly, selection of pipes for the

construction of piping systems should be based on the design conditions such as the

pressure, temperature of the material to be transported, the velocity: mass flow rate and

volumetric flow rate of the materials to be transported, and the composition of the
 material to account for the corrosion and erosion. Generally, there are standard piping

codes that serve as guides for proper selection of piping material, example of such is the

ASME Code for Pressure Piping. The importance of identifying the correct material for

the pipes is to ensure that they will operate safely under the specified conditions at which

they are designed for or being selected for. Listed below are the most common piping

materials available:

 Steel – can be forged or casted, manufactured under two categories: seamless and

Welded

 Cast Iron – high resistance to corrosion and abrasion, yet very brittle and not

suitable

for plant services

 Brass & Copper – both are non-ferrous materials which made them perfect for

water

distribution services

2.2. Pipe Sizing

Dimension or size of a pipe corresponds directly to its strength thus it is an important

factor to be considered in pipe design. Commercially available pipes are made in

standard sizes and is designated by its nominal pipe size (NPS) or the inner diameter

(ID). These standard measurements allow piping system engineers to have a rough

indication of the pipe conveyance capacity. Traditionally, an older method is being used

to designate pipes such as (S) for Standard, XS for extra strong, and XXS double extra

strong. But in the present new method are being used which is considered better that the

previous method. It uses schedule numbers that indicates wall thickness of the pipe.
 These numbers are the following: 10, 20, 30, 40, 60, 80, 100, 120, 140, and 160. Shown

in the figure below are the common pipe schedules and weights.

2.3. Pipe Fittings

The lengths of commercially available pipes are standard hence to construct piping

systems that span hundred to thousand meters of piping, fittings are used to connect

them. Pipe fittings also allow pipes to change direction and conforms to places where

they will be installed. Common pipe fittings used are shown in the figure below.
  Elbows – used for making angle turns

 Couplings – used for connecting two pipes of similar size

 Unions – used for easy dismantling of pipes

 Tees & Crosses – used for branching lines

 Plugs & Caps – used for closing the ends of open pipes

 Nipples – used for making close connections

 Reducers – used for reducing pipe size

2.4. Pipe Connection Methods

As mentioned in the previous section, length of pipes are standard hence connecting of

pipes to lengthen it is common, and there are methods used to do it. Generally, there are

three methods used, namely:

 Screwed Connections

 Flanged Connections

 Welded Joints
 Using screwed connection method, threads are made on the ends of pipes to connected.

Then threaded fittings such as couplings, elbows, and unions are used to connect them.

This method is advised to be used for low to moderate pressure operations only.

Disadvantages are it is prone to leakage, and the strength of the pipe reduces due to the

removed portions for the thread.

Using flanged connection method, flanges are used to connect ends of the pipes, and is

bolted together using nuts and bolts. Major advantage of this method is the convenient

assembly and disassembly. To prevent leakage between connections, gaskets are used.

Using welded joints, pipe ends are directly welded to each other. Major advantages of

using this method is the elimination of possible leakage as there are no mechanical joints

already. Moreover, weight of the pipe is reduced as well, and the finished connected is

much neater. Only disadvantage is that to be able to have good, welded joint, a skilled

and professional welder must be obtained every pipe connection.

3. PUMP SELECTION

Design of piping system also includes the selection of pumps to be used to optimize

its operating efficiency and life expectancy. Three factors that are being considered in

selecting the right pumps are the NPSH requirements, suction piping, and location.
3.1. Net Positive Suction Head Requirement

The NPSH margin is an important variable to consider in selecting pumps. It is defined

as the difference between the available NPSH in the inlet of the pump, and the required

NPSH by the pump in order to operate without cavitation. It is important that there must

be no cavitation as it causes permanent damage on the pump. To avoid cavitation, NPSH

margin value must always be positive. As mentioned earlier, NPSH required and NPSH

available are the two parts that are being considered for the NPSH margin. The required

NPSH refers to the minimum pressure necessary in the suction inlet of the pump to keep

it from cavitating. Furthermore, the available NPSH refers to the absolute pressure in the

suction inlet of the pump.

3.2. Suction Piping

Generally, suction piping size should be at least one size larger than of the pump suction

nozzle. Due to the size difference, reducers are used and must be installed as close to the

nozzle as possible. When eccentric reducers are used, it is very important to place the

flat side on top (for horizontal pipelines). This is to prevent air from being trapped in the

reducer which can lead to major pump damage if happens.

Commonly, pumps are placed below or adjacent to the pipe racks. Moreover, if multiple

pumps are considered, arrange them in such a way that maintenance possible if needed

be, the advisable width of the aisle is 2 m to 2.5 m. Materials and composition of the

fluids to be pumped is necessary to consider as well. If the material being pump is

flammable, it should not be placed near pipe racks, and other equipment. Similarly, high

pressure pumps also impose similar threat hence it should be place separately from low

pressure pumps and other less harsh equipment.

3.4. Common Industrial Pumps

Geothermal piping design refers to the concept of designing pipelines to transport steam and

brine safely and economically with acceptable pressure loses. In geothermal powerplants,

piping is divided into two: piping inside the power plant, and piping in the steam field. Piping

in the steam field specifically refers to the pipelines that connect production wells and

injection wells, that run to the powerplant. Because these production wells and injection

wells commonly located relatively far from the powerplant, it runs through cross-country that

have ridges, steep hills, and crossroads which will affect pump performance and efficiency.

Also, because geothermal piping runs through the cross-country, pipelines should be flexible

to allow for thermal expansion, yet rigid enough to withstand seismic and operational load

actions.

In wet steam field system, two-phase flow piping is used: one that collects fluid from several

wellhead, and the other send to the separator. In the separator vessel, steam pipelines take the

steam from the separator to the powerplant. On the other side, brine pipelines take the

separated brine from the separator to the wellpads where they will re-injected into the

injection wells. Other pipelines include equipment air/pneumatic lines, water supply, and

condensate lines.
4.1. Design Considerations

In designing piping system, the crucial part in the design process is establishing the

design conditions and criteria as it will dictate how each component will be selected and

installed in the field. To determine the design conditions, one of the factors that need to

be considered is the characteristics of production wells and re-injection wells in the

steam field. The output characteristics, mass flow rates, well head pressure, and

temperature need to be considered as it will affect the whole project for its entire

lifespan. In the transportation of steam from the separation station to the powerplant,

heat losses and pressure losses are expected to happen as well. So, to determine the

diameter of the pipe needed and thickness of the insulation, the working equation for

open and steady system is shown below:

Where:

Q = Rate of heat transfer

W s = Rate of work transfer

i = index that runs over all inlets and outlets

n = total number of inlets and outlets

m i = mass flow rate on each inlet and outlet

hi = specific enthalpy of the fluid

V i = velocity of the fluid

g = local gravitational acceleration (commonly 9.81 m/s^2)

For the conservation of mass:

To determine the pressure drop, heat losses and the electric power output for a given

power capacity and size of steam pipe, use the following equations:

For the friction losses in the pipe and fittings:

For pipe friction:

For the electric output:

Where:
4.2. Piping Design

In piping design for geothermal powerplants, determination of the problem is necessary,

which includes the characteristics and composition of the fluid to be carried, in this case

—steam and ground particles and impurities, also the flow rate, and the allowable

headloss. Next is the location and routes that will be taken by the pipelines considering it

will run through cross-country roads where terrain cannot be expected to be flat.

Moreover, the design code to be followed must be strictly implemented as well. Lastly,

in the materials to be used.

Pipes need to be sized correctly and run flat or on a downhill slope to achieve annular

flow. Uphill sloping pipes are not desirable as this causes slugging in the pipe. The

steam and water flow patterns in the pipe vary from annular, to slug, to open channel

flow. Slug flow causes high dynamic load and vibration that can damage the piping

system. So, the preferred flow regime in the pipes is usually annular flow.

CONCLUSION

In the Geothermal Powerplant engineering, in can be greatly observe the importance of

designing piping system and proper selection of pumps to be used as there are many factors that

need to be considered for the whole plant to function and operate safely, efficiently, and

economically. Moreover, in-depth understanding of the application of fluid machineries is

essential to all mechanical engineers because it is said that piping system is the lifeline of the

manufacturing industry. Determining the design conditions for specific projects requires

knowledge in threshold of every parameters that are being considered. Material should be able to

conform with the natural changes like thermal expansion and contraction, and seismic

movements of the ground. Elements to be selected must be capable of operating beyond the
nominal operating conditions of the project in order to compensate for sudden changes that may

occur such as power surge, increase pressure, or well blowout, and/or leak. But on top of all of it

because this is in real-world application already, the main purpose of proper pipe design and

pump selection is cost. By proper identification of the necessary materials and equipment to be

acquired, the project will not be overly-engineered and/or under-engineered—which may cause

catastrophic consequences in the future.

REFERENCES

1. https://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322000000400053

2. https://petrowiki.org/Pipeline_design_consideration_and_standards

3. https://www.aiche.org/sites/default/files/cep/20161238_r.pdf

4. https://www.piping-world.com/pump-piping-layout-and-design

5. https://www.theprocesspiping.com/introduction-to-piping-system/#:~:text=A%20pipe
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6. file:///C:/Users/Asus
%20Pc/Downloads/Optimal_Design_of_a_Pump_and_Piping_System_Second_Submissi
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7. http://www.pumpengineering.net/blog/industrial-pump-types-benefits-application/

8. https://www.pumpsandsystems.com/topics/understanding-npsh-npsh-
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%20the%20pump%20running

9. https://www.springerpumps.com/productnews/npsh-net-positive-suction-head-
matters/#:~:text=NPSH%20or%20Net%20Positive%20Suction,that%20depend%20on
%20that%20pump.