NBSIR 74-505

Tests of a Grease Interceptor

Similar to Those Used in Galleys

C. M. Hunt, D. R. Showalter, and S. J. Treado

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

March 25, 1974

Final Report

Prepared for Commander, Naval Ship Systems Command

(Ships 053)

Washington, D. C 20350

NBSIR 74-505

TESTS OF A GREASE INTERCEPTOR

SIMILAR TO THOSE USED IN GALLEYS

C. M. Hunt, D. R. Showalter, and S. J. Treado

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

March 25, 1974

Final Report

Prepared for Commander, Naval Ship Systems Command

(Ships 053)

Washington, D. C. 20350

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Tests of a Grease Interceptor Similar to Those Used in Galleys

C. M. Hunt, D. R. Showalter, and S. J. Treado

Thermal Engineering Systems Section

Center for Building Technology

Institute for Applied Technology

ABSTRACT

Apparatus and methods have been developed for evaluating grease interceptors of the type used over cooking ranges. They have been applied

to an interceptor which is in common use in ships' galleys as well as restaurants. The tests include evaluation of resistance to airflow,

efficiency in removing airborne grease droplets, and effectiveness of

the internal cleaning mechanism. These tests are intended to be an aid

in developing specifications for grease interceptors.

Key Words: Aerosol interceptor; droplet interceptor; filter;

grease; grease interceptor

i
Table of Contents

Page

1. Introduction 1

2. Description of Grease Interceptor 1

3. Description of Test Apparatus and Test Methods 1

a. Determination of Resistance to Airflow 1 b. Determination of Efficiency 2 c. Washing Tests 3

4. Results 3

a. Flow Resistance 3

b. Efficiency , 3 c. Effectiveness of Washing 4

Tables 5

Figures 9

ii
1. Introduction

At the request of the Commander, Naval Ship Systems Command, tests

were performed on a grease interceptor of the type used in kitchens and

galleys. The scope of the tests included determination of resistance to

airflow and efficiency in removing grease droplets from the air. Tests

of the effectiveness of the internal washing mechanism of the device were

also made.

2. Description of Grease Interceptor

The grease interceptor in these tests was an inertial type of cleaning device. When air was drawn through it in normal operation, grease

droplets were deposited on its internal baffles. A manufacturer's diagram of a cutaway side view of the apparatus is shown in Figure 1. The

particular model tested was four feet wide.

The grease interceptor was equipped with an internal washing system

in which water entered through a connection in the back and fed a number

of spray jets inside the device. The position of the jets is indicated

in Figure 1 as projections on baffles 2 and 4, but they are not labelled.

3. Description of Test Apparatus and Test Methods

A transition and upper chamber were mounted over the take-off collar

of the grease interceptor. A working diagram of this part of the apparatus is shown in Figure 2 . In operation the filter medium was drawn

against the wire cloth backing with a tight seal. The reinforcing rods

and filter support wires in the actual apparatus were oriented 90° in

the horizontal plane from the position shown in Figure 2. A photograph

of the test apparatus is shown in Figure 3. The apparatus was connected

to a test duct by a flexible trunk shown at the left in this figure.

a. Determination of Resistance to Airflow

Flow velocity was measured by means of an 11-inch (27.9 cm) orifice

plate mounted 7 feet (2.1 m) downstream from the entrance to the duct.

Pressure drop across the orifice was measured with an inclined manometer

which was calibrated against a Hook gage. Measurements were repeated

using a 7-inch (17.8 cm) orifice and a flow nozzle respectively as flow

measuring devices instead of the 11-inch orifice. This provided an independent check of flow in regions where the flow ranges of the three

devices overlapped.
Four pressure taps were placed symmetrically on the two sides and

the front and back of the lower transition shown in Figure 2 , at a level

1 1/2 inches (3.8 cm) above the take-off collar of the grease interceptor.

The average pressure at these taps was compared with the atmospheric pres- sure in the room as a measure of resistance to airflow.

b. Determination of Efficiency

In a National Bureau of Standards Report of March 18, 1954, Coblentz

and Achenbach noted that droplets produced by a paint spray apparatus were

similar in size to those collected in an actual cooking operation aboard

ship. Since a paint spray gun affords an easy way to produce a comparatively high delivery rate of droplets, one was used for the present tests.

A picture of the device is shown in Figure 4. A special clamp and holder

which is shown in the figure was mounted on the spray gun to hold it in

the open position. A diagram of the various components of the gun is

shown in Figure 5

The gun was mounted in a laboratory built heater which consisted es- sentially of a nichrome wire wound on a Teflon spacer mounted in the annular space between two brass cylinders. It was insulated at the top and

bottom with dense fiber glass and surrounded the reservoir of the spray

gun with a clearance of about 1 mm. The heater may be seen in the lower

left portion of Figure 3 partially obscured by the nitrogen tank. The

temperature of the heater was controlled by means of a Micromax* temperature controller which responded to a copper-constantan thermocouple mounted

in the inner surface of the heater. The temperature of the grease was measured by a thermocouple mounted directly in the grease. The grease

interceptor was operated at room temperature which is cooler than in a normal cooking operation.

Compressed nitrogen was used to disperse the grease in the efficiency

measurements. However, it was felt that the difference between the use of nitrogen and air was minimal, and compressed air was used for loading

the interceptor prior to the washing tests. The spray was directed horizontally (from left to right in Figure 3) across the front of the device.

A mercury manometer was used to measure the spray pressure, since the

pressures, which were of the order of 15 to 30 cm of mercury, were less

than those normally used in paint spray operation.

Certain commercial materials and instruments are identified in this

report in order to specify experimental procedure adequately. Such

identification does not imply recommendation or indorsement by the

National Bureau of Standards, nor does it imply that the equipment

or material identified is necessarily the best for the purpose.

2
The amount of grease fed during a single test was determined by

weighing the reservoir at the beginning and end of each measurement.

Twelve minutes were arbitrarily selected as the time for each grease

feeding operation. The grease passing through the interceptor was captured on an Owens -Corning* PF 105 fiber glass medium which was weighed

at the beginning and end of each measurement

c. Washing Tests

A tee similar to that shown in Figure 6, with 3 valves and a pressure

gage, was attached to the grease interceptor. Water temperature was measured by means of a copper-constantan thermocouple in the line. The washing procedure consisted of successive two-minute periods in which water

of controlled temperature and pressure was flushed through the interceptor,

and an inspection was made after each washing period. All tests were performed without a detergent

4. Results

a. Flow Resistance

The average pressure drop across the grease interceptor as a function

of airflow rate is given in Table 1, and the data are presented graphically

in Figure 7. Pressure drop was also measured in the upper part of the

grease interceptor (transition area in Figure 1), and it was usually about

4 to 8 percent less than the values given in Table 1 which were measured

1 1/2 inches (3.8 cm) above the take-off collar. At the rated velocity

of 1000 cfm (28.3 m^/min.) the pressure drop was approximately 1.5 inches

W. G. (.0025 bars).

b. Efficiency

The efficiency data are summarized in Table 2. As explained in the

footnote at the bottom of the table, the uncorrected efficiency is based

on the fraction of grease fed which is not captured by the back-up filter.

The corrected efficiency treats that fraction of the grease which settles

on the floor and sides of the grease interceptor up to a height of about

1 ft as grease which was never fed to the device. It was felt that this

Certain commercial materials and instruments are identified in this

report in order to specify experimental procedure adequately. Such

identification does not imply recommendation or indorsement by the

National Bureau of Standards, nor does it imply that the equipment

or material identified is necessarily the best for the purpose.

3
fraction of the grease might be more responsive to feed rate and method

of feeding than grease encountered in normal operation.

Most of the uncorrected efficiency values were between 93 and 96 percent while the correct values were almost a percent less. The measurements were made at flow velocities of 1000, 1100, and 1200 cfm. There

was evidence of a slight increase in efficiency with increasing air speed,

but the differences were close to normal experimental error.

It should be noted that there was considerable variation in the feed

rate from run to run as shown in Table 2. This was primarily because the

feed rate was very responsive to small changes in the setting of the trigger of the spray gun. It is possible that for this particular application

some simpler device might be constructed which would have fewer adjustments than a commercial paint spray gun. However, with the exception of one value which was obtained at a very low rate of feed, differences in

feed rate of the magnitude shown in the table did not appear to have a significant effect on efficiency.

In three separate runs a high volume sampler with high efficiency

glass fiber paper was placed in the port of the upper chamber of the test

apparatus shown in Figure 2. Samples were collected to determine whether

there was escape of droplets through the back-up filter. The data indicated that less than 0.1 percent of the grease droplets fed into the interceptor passed the back-up filter.

c. Effectiveness of Washing

The results of the washing tests are shown in Table 3. At 30 psi

and water temperature of 160 - 165 °F all heavy deposits of grease were

removed within the first two minutes, while at 135 - 137 °F at the same pressure, an additional two minute washing period was required. At water

temperature of 118 - 124 °F and a pressure of 15 psi, deposits remained

after five washing periods, and the cleaning was not fully effective when

the pressure was raised to 30 psi. These latter measurements were made

to observe cleaning performance below manufacturer's recommended temperature and pressure.

There was a thin deposit of grease near the take-off collar which

was out of the range of the washing sprays in all measurements. However,

it is probable that under the conditions of operation when the unit is

operated hot as in cooking, there would be little deposit here.

4
Table 1

Resistance to Airflow - Pressure Drop as a Function

of Flow Velocity through the Grease Interceptor

Flow Rate Ap

(cfm) Across Interceptor

(in. W. G.)*

11" Orifice 860 1.16

1020 1.62

1100 1.86

1245 2.33

7" Orifice 760 0.81

940 1 . 28

1000 1.50

10" Nozzle 908 1.36

1060 1.81

W. G. = water gage

5
Table 2

Efficiency of Grease Hood in Intercepting

Grease Dispersed by Paint Spray Apparatus

Efficiency

(percent)

Efficiency

Corrected

(percent)

Average

Feed

Rate

(g/hr)

Average

Temperature

of Grease in

Spray Gun

°F

1000 cfm

93.

95.2

93.9

average 94.1

91.8

94.6

93.1

93.2

102

73

122

193 - 198

197 - 198

1100 cfm

95.0 94.9 87 199

94.7 93.8 68 198 - 202

94.3 93.8 127 199 - 200

95.1 94.2 67 200 - 202

94.8 94.3 102 200 - 202

average 94.8 94.3

1200 cfm

95.0 93.6 58 197

93.8 91.9 65 198

94.9 94.4 220 198 - 201

96.4 95.8 134 199 - 200

96.5 95.9 79 198 - 200

96.5 96.0 85 196 - 197

95.6 94.0 137 203

96.3 95.

C 95 199 - 200

98.3° 96.5 47 196 - 198

average 95.6 94.5

6
b Efficiency = H

d -

V'f x 100 wd

W z wt. gain of back-up filter

W, s wt . of grease dispersed

Efficiency

correc ted

(wd

- C) - W

f x 100

. - c

c = wt. grease collected on floor of grease interceptor

and on sides up to 1 ft

c Omitted from average because of slow feed rate and large amount

of grease collected on walls and floor of hood

7
Table 3

Schedule of Washing Tests and Results

1st Washing Test @ 330 g grease fed to grease hood prior to test.

2 minute Temperature Pressure Observations

Washing °F psi

Period

1st 162 - 165 30

2nd 161 - 163 30

3rd 159 - 161 30

All heavy deposits of grease

removed in 1st 2 minutes.

2nd Washing Test @ 360 g grease fed to grease hood prior to test.

1st 135 30 Two deposits of grease, one

2nd 136 - 137 30 7 mm in diameter and one

1.5 mm remained after 1st

2 minutes. Removed in 2nd

2 minute period.

3rd Washing Test @ 270 g grease fed to grease hood prior to test.

1st 118 15 There was some reduction in

2nd 119 15 amount of grease, but

3rd 120 - 121 15 significant deposits re- 4th 120 15 mained after the first five

5th 121 - 122 1Z 2-minute periods. One

6th 123 20 deposit, 5 cm in diameter

7th 123 - 12-' 20 remained even after the 10th

8th 12? - 124 25 2 minute washing period.

9th 122 - 123 30

10th 122 30

8
surface merges with the cool blanket of air, then

pasr.e

,; through the grease extracting chamber where

the gr .e is removed by centrifugal fore-:?.

Figure 1 Manufacturer's Diagram of Cutaway Side View

of Grease Interceptor

9
PORT FOR HI -VOL SAMPLER

TO TEST DUCT

3-

REINFORCING

^ ROD

HINGED ARTICULATION BETWEEN

UPPER CHAMBER AND LOWER

TRANSITION NOT SHOWN

UPPER CHAMBER

GASKET

WIRE CLOTH FILTER

BACKING

FILTER MEDIUM (1.22 m x 1.22 m)

FILTER SUPPORT

WIRES

LOWER TRANSITION

FROM

GREASE

HOOD

SUPPORT FRAME NOT

SHOWN

Figure 2 Diagram of Apparatus for Capturing

Grease From Grease Hood

10
Figure 3 Picture of Grease Interceptor Mounted in the Test Apparatus

SPRAY GUN

Figure 5 Diagram of Components of Spray Gun 13
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14
PRESSURE DROP ACROSS GREASE HOOD AS FUNCTION OF

FLOW RATE

O II INCH ORIFICE

A 10 INCH SHAPED NOZZLE

V 7 INCH ORIFICE

J L. I I I I I LLU I I I I I I I I

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o o oo o ooo ooo o o oo — ojcjro <f m (o n co o>o— m— cJ^ro o^o ooooooo ^-mcDNOO <t>q

FLOW RATE (CFM)

Figure 7 Pressure Drop Across Grease Intercr-ptor as a Function of Flow Rate

15

FORM NBS-1 14A (1-7U

• u.s. dept. of comm. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA ms IR 74.505 No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Tests of a Grease Interceptor Similar to Those Used in

Galleys

5. Publication Date March 25, 1974

6. Performing Organization Code

7. AUTHOR(S)

C. M. Hunt, D. R. Showalter, and S. J. Treado

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4623648

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Commander, Naval Ship Systems Command

(Ships 053)

Washington, D. C. 20350

13. Type of Report & Period

Covered

Final

14. Sponsoring Agency: Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Apparatus and methods have been developed for evaluating grease interceptors of the

type used over cooking ranges. They have been applied to an interceptor which is in common use in ships' galleys as well as restaurants. The tests include evaluation of

resistance to air flow, efficiency in removing airborne grease droplets, and effective ness of the internal cleaning mechanism. These tests are intended to be an aid in

developing specifications for grease interceptors.

1 7. key words (Alphabetical order, separated by semicolons) aerosol interceptor; droplet interceptor;

filter; grease; grease interceptor

18. AVAILABILITY STATEMENT

I I UNLIMITED.

I77TFOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

12

22. Price

U5COMM-DC 66244-P7?