API 421 : 1990

Section 1 - General
1.1 Introduction
1.2 Background
1.3 Basic Theory
1.4 Application
1.5 Referenced Publications
Section 2 - Conventional Oil-Water Separators
2.1 Design Procedures
2.1.1 General
2.1.2. Wastewater Characterization
2.1.3 Establishing a Design Flow
2.1.4 Step-by-Step Design Calculations
2.1.5 Design Example
2.2 Construction Details
2.2.1 General
2.2.2 Inlet Section
2.2.3 Separation Section
2.2.4 Other Design Features
2.3 Performance
Section 3 - Improving the Performance of Existing
            Separators
3.1 General Approach
3.2 Process Troubleshooting
3.2.1 Design Review
3.2.2 Emulsified Oil
3.2.3 Flow Surges
3.3 Dealing with Emulsified Oil
3.4 Retrofitting Existing Separators with Parallel
      Plates
Section 4 - Parallel-Plate Separators
4.1 General
4.1.1 Introduction
4.1.2 Design
4.1.3 Wastewater Characteristics Required for
        Separator Sizing
4.1.4 Parallel-Plate Surface Area
4.1.5 Maintenance
4.2 Construction Details
4.3 Performance
Section 5 - Operation and Maintenance of Oil-Water
            Separators
Section 6 - References
Appendix A - Derivation of Basic Equations for Design
             of Oil-Water Separators
Appendix B - Determination of Susceptibility of
             Separation
Appendix C - Selected Results: 1985 API Oil-Water
             Separator Survey
Appendix D - Test for Specific Gravity of Oil in
             Wastewater
Figures:
1. Specific Gravity of Clear Water (Fresh and Sea) for
    Temperatures between 40 deg F and 120 deg F
2. Absolute Viscosity of Clear Water (Fresh and Sea)
    for Temperatures between 40 deg F and 120 deg F
3. Design Variables for Oil-Water Separators
4. Recommended Values of F for Various Values of vH/Vt
5. Conventional Oil-Water Separator (Uncovered)
6. Reaction-Jet Inlets
7. Vertical-Slot Baffle
8. Four-Shaft Collector-Type Oil- and Sludge-Moving
    Device
9. Traveling-Bridge Oil Skimmer and Sludge Collector
10. General Arrangement of Rotatable Slotted-Pipe
    Skimmer
11. Rotary-Drum Oil Skimmer
12. Horseshoe-Type Floating Skimmer
13. Self-Adjusting Floating Skimmer
14. Covers for Oil-Water Separators
15. Performance of Conventional Oil-Water Separators
16. Correlation Between Influent and Effluent Oil Levels
    for Existing Oil-Water Separators
17. Cross-Flow Parallel-Plate Separator
18. Downflow Parallel-Plate Separator
19. Performance of Parallel-Plate Separators
Tables
1. Applicability of EPA Methods 413.1 and 413.2
2. Typical Ranges for the Basic Design Variables of
      Parallel-Plate Separation
C-1. Selected Results of 1985 API Oil-Water Separator
      Survey: Conventional Separators
C-2. Selected Results of 1985 API Oil-Water Separator
      Survey: Parallel-Plate Separators
D-1. Oil-Density Variation with Temperature (15 deg API
      - 35 deg API)

Provides design guidance for gravity-type oil-water separators for use in petroleum refineries, provides practical advice on solving operating problems and improving separator performance, and presents information on performance of existing refinery separators. Coverage includes: conventional oil-water separators (features wastewater characterisation, inlet selection and separation section); improving the performance of existing separators (features process troubleshooting, emulsified oil, flow surges, and retrofitting existing separators with parallel plates); parallel-plate separators (features construction details, maintenance, parallel-plate surface area, and wastewater characteristics required for separator sizing); operation and maintenance of oil-water separators.