Table of Contents. Foreword... xvii Executive Summary... xxi. Chapter One Pump Fundamentals, 1

Transcription

1 Foreword xvii Executive Summary xxi Chapter One Pump Fundamentals, Introduction How a Rotodynamic (Centrifugal, Mixed Flow, and Axial Flow) Pump Works Basic Pump Configurations and Arrangements Pump Drives (Fixed Versus Variable Speed) Pump Selection Considerations Understanding the Pump Performance Curve Types of Curves Total Head Versus Rate of Flow Pump Efficiency Net Positive Suction Head Shut-off (Closed Valve) Head Minimum Flow Allowable Operating Region (AOR) Best Efficiency Point (BEP) Preferred Operating Region (POR) Maximum Flow (Pump Runout) Pump Suction Intake Considerations Location of Pump in the System Pump Suction Piping Liquid Properties Supply Tank and Atmospheric Pressure Pump Affinity Rules Changes in Rotational Speed Changes in Impeller Diameter Operation of Pumps Chapter Two Pump and System Interaction, Introduction v

2 vi Optimizing Pumping Systems 2.2 The Basic Calculations Bernoulli Equation Pipe Run Head Loss Using the Darcy-Weisbach Equation The Piping System The Pipe Runs Components The Pump Curve Affinity Rules Control Valves System Curves What is a System Curve? How System Curves Are Used Friction Dominated Systems Closed Example Effect of Elevation Differences Static Head Dominated Systems Varying the Flow Rate Using a Control Valve Manual Throttling Valves Changing the Pump Curve Example of Impeller Changes with a Control Valve in the System Pump Efficiency Effects Multiple Pump Operation Effects of Changes in System Operation Condition How to Create a System Curve Single-Pump Systems Multipump Systems: Pumps in Parallel Multipump Systems: Pumps in Series How to Handle Control Valves How to Handle Check Valves Complex Piping Systems Conclusion Chapter Three Calculating Cost of Ownership, Introduction Replacement Expansion

3 vii Growth Other Elements of Life Cycle Cost Initial Cost Installation Cost Energy Cost Maintenance Cost Operating Cost Downtime and Lost Production Cost Environmental Cost Decommissioning Cost Analyze Life Cycle Costs (LCC) Before Making a Decision Investment Justification and Decision-Making Return on Investment (ROI) The Payback Method Calculating the Average Rate of Return Time Value of Money Calculating Net Present Value Calculating Internal Rate of Return Looking at ROI from a Broader Perspective Chapter Four Improving the Performance of Existing Pumping Systems, System Types Prerequisite Correct Existing Operational Deficiencies System Problems Assessing the Current System Diagnostics and Data Collection Data Collection Collecting/Determining Pumping System Energy Cost Collecting Performance Data Using the Data to Identify Opportunities Comparing Pump Data to Performance Curve Calculating Energy Costs Due to Passive Throttling Devices Bypass control Evaluating Proximity to BEP: Pump Duty Point Matching Pump and System

4 viii Optimizing Pumping Systems Using Pump System Modeling Tools or a Consulting Expert to Extend Performance Data Compare Operating Data to Original Data Multistage Pumps Evaluating Opportunities Specific Energy Comparing Component Data Variable Speed Operation: The Need for Performance Variation Pumping Systems Control Variable Speed Control Pump Control by Varying Speed Varying Speed in a System with Only Friction Head Varying Speed in a System with High Static Head Other Implications of Varying Speed Flow Control: Pumps in Parallel Switched to Meet Demand Stop/Start Control Multiple, Staged Pump Operation, Pumps in Parallel and Series Pump Replacement/Upgrade Using Pump System Modeling Reducing Energy Usage and Magnitude of Nonenergy Benefits Application Example Getting Started on Optimizing Your Pumping Systems to Gain Significant Benefits Numerical Example of BEP Evaluation and System Modification Options Summary Chapter Five Building Better Pumping Systems: Optimizing New Designs, Opportunities Available In New Systems Competing Effects of Initial and Life Cycle Cost Variables Available to the Pump System Designer Operating Points Have Costs

5 ix Comparing Opportunities Between Existing and New Systems The Optimal Operating Point Conceptual Example Optimal Pumping System Operating Point Finding the Optimal Design How Pumping Systems Change Over Time Passive Influences Change in Pipe Diameter Change in Capacity Requirements Change in Static Head Wearing of Piping Components Wearing of Pump Components Active Influences The Value of Modeling and Optimizing New Designs Before Construction Commercial Accountability First Cost Versus Life Cycle Costs Plan for Immediate Improvements Pump Design Considerations in New Build Systems Selecting for Maximum Attainable Efficiency Impeller Trim Pump Construction Specification Pump Corrosion/Erosion/Fouling Pump Design Speed Pump Type: Single Stage or Multistage Submersible or Vertical Turbine Nozzle Inserts and Diffuser Rings Design for the Future Communications Piping Design Pump Selection The Design Flow Rate with Control Valve The Lower Expected Flow Rate with Control Valve Variable Frequency Drives Margin in System Design: Intentional or Unintentional? Control Scheme Optimization - Getting It Right the First Time Liquid Levels Speed Range Verification of Flow and Pressure Control Device Parameters Variable Speed Drive/System Control Options

6 x Optimizing Pumping Systems Chapter Six Pumping System Economics: Opportunities to Improve LCC, Introduction Scope of the Opportunity Potential Energy Savings Why Improvement Opportunities Exist Lack of a Systems Approach During the Design Process Overly Conservative or Improper Pump Selection Improper Installation or Operation Poor Maintenance System Requirements Change Over Time Making a Business Case Appeal to Management s Profit Motive Relate Savings to the Plant s Bottom Line Support with Financial Analysis Look Beyond Energy Savings Attach Dollar Values to Nonenergy Benefits Life Cycle Costing Analyzing from an Integrated System Perspective Summary of Alternatives (Examples) Conclusion Appendix A Glossary, 189 Appendix B References, 203 Appendix C Optimizing Pumping Systems Case Studies, 205 C.1 Introduction C.2 Case Study C.3 Case Study C.4 Case Study

7 xi C.5 Case Study C.6 Case Study C.7 Case Study C.8 Case Study Appendix D Acronym Table, 227 Appendix E Tool Matrix, 231 E.1 Pump, Driver, and System Assessment Tools E.1.1 Valve Tools E.1.2 Piping System Tools E.1.3 Pump System Assessment Tools E.1.4 Motor Tools E.1.5 Variable Frequency Drive Assessment E.1.6 Life Cycle Cost Tools E.1.7 Seals and Environmental Controls E.1.8 Other Tools Appendix F Index, 245 List of Figures 1 Overview of industrial motor systems optimization opportunities xxii 2 Example rotodynamic pump and system curves xxiii 3 Example life cycle costs for a pumping system xxvii 1.1 Rotodynamic pump configurations Example selection chart Example pump curve Pump performance curve at test speeds of 1770 and 1500 rpm Graph of head loss versus rate of flow When pipe runs are in series, the head losses for the individual pipe runs are added to generate a head loss curve for the multiple pipe runs The balanced flow rates in a parallel path must meet both the flow and pressure loss requirements of Kirchoff s laws

8 xii Optimizing Pumping Systems 2.4 The balanced flow rates through pipe runs in parallel can be graphically solved Changing the rotational speed of a centrifugal pump changes the shape of the pump curve Changing the impeller diameter of a centrifugal pump changes the flow and head of the pump curve System curve shown with pump curve System curve resulting from only friction A closed recirculation system diagram indicating flows and head losses The intersection of the pipe run resistance curve and the pump curve is the balanced flow rate through the piping system Effect of elevation changes on system curve Systems curve before and after an elevation increase Static head dominated system curve A flow control induces a pressure drop to achieve a desired flow A manual throttling valve increases resistance and shifts the system curve to the left Increasing the impeller diameter causes an increase in flow rate through the system Changing the speed of the pump impeller changes the flow rate by changing the intersection of the pump and system curves PSIM model for which system curves will be created before and after impeller trimming Pump system curve for original impeller size Pump system curves for reduced impeller size Pump and system curves with the pump efficiency curve included Iso-efficiency lines on a head/flow diagram follow the behavior of head (quadratic) and flow (linear) Friction dominated system curves parallel pump iso-efficiency lines Static head dominated system curves do not parallel iso-efficiency lines Composite pump curve with multiple pumps in parallel. Here each pump has an identical pump curve

9 xiii 2.26 Steep system curve superimposed on a composite pump curve with parallel pumps Shallow system curve superimposed on a composite pump curve with parallel pumps An example of two dissimilar pumps running in parallel Composite pump curve with multiple pumps in series How three pumps in series operate Varying the static head in the piping system varies the flow rate through the pump as shown on the pump and system curves PSIM model for creating a system curve System curve graph using the Table 2.5 data PSIM model for creating a system curve Composite system curve graph using the Table 2.6 data and taking an average head A relatively small system with a single pump and three parallel paths with flow control valves to limit the flow rate through each path to a set value Pump System Prescreening Form Power consumption and cost of electrical motors Simple energy cost calculation Direct measurement Boiler feed system indicating intermediate take-off flow and pump speed Boiler feed system simulating flow path to economizer and suction from condenser Condensate feed system Typical pump performance curve with two data points Flow control valve Bypass valve Pump and system curves intersection point System curve with a pump head curve and efficiency curve Closed loop in decision making Energy consumption Pump controlled by varying speeds

10 xiv Optimizing Pumping Systems 4.16 Example of the effect of pump speed change in a system with only friction loss Example of the effect of pump speed change in a system with high static head Typical curves for pumps in parallel, with a system curve Unstable axial flow pump curve versus unstable radial pump curve Typical curves for pumps in series System to supply cooling water to two heat exchangers Composite pump and systems for original systems and all modifications considered Key cost components for a pumping installation as related to pump size An operating point on pump and system curves has a cost associated with it Pump selection, including the impeller size and speed, affects operating point by shifting pump curve Using variable speed pumping, the effective pump curve can be shifted, which will change the operating point Changing the system curve will change the operating point, and it is most easiliy done during the design phase Comparison of existing and new system change opportunities When designing a new system, what is the optimal operating point? Conceptual cooling-water system Estimated costs for flows of 1800 m 3 /h (8000 gpm) at different TDH for conceptual example Estimated costs for pipes from 4 to 48 in for conceptual example Pump and system curves, for initial design of conceptual system Changing operating point of conceptual system will involve changing the pump curve and/or system curve but flow will remain at required 7270 m 3 /h (32,000 gpm) Pipe sizes before and after conceptual system optimization using 130-kW (175-hp) pumps Pipe sizes before and after conceptual system optimization

11 xv 5.15 Curve of optimum designs for various pump sizes and OPSOP for conceptual system Flow chart depicting computer-based optimization methods coupled with conventional pump system modeling tool Attainable efficiency a Multistage tandem (in-line) impeller arrangement b Multistage opposed (back-to-back) impeller arrangement Volute inserts can adjust the pump BEP and allow increased operating range with high efficiency The open-loop piping system used in the system optimization example Distribution of motor system energy use by application Causes of production losses in refineries Sources of unscheduled shutdowns in oil and gas facilities Summary of alternatives List of Tables 1 Symptoms of an inefficient pumping system xxiv 2.1 Isolation valve configurations/losses Pump performance data Calculated results for full-size impeller Calculated results for 10% reduced impeller Data points for system curve generation Data points for system curve generation The flow rate and valve position through each branch of a hydraulic network varies as the changes are made Expected cash flows based on two different investment alternatives Net present value calculation Internal rate of return calculation System improvement options Valve types with typical head loss and the resulting pumping costs for the losses Pump failure modes Distribution of motor system energy use by application