Development of Oil Refinery Waste Reduction Technology

1

[M3.1.8]

Development of Oil Refinery Waste Reduction Technology

(Excess sludge solubilization group)

� Hitoshi Kumagai, Hiroaki Ohtsuka, Keitaro Watanabe,

Shigeyuki Watanabe, Toru Yoshii, Mitsunori Matsumoto

1. R&D Objectives

The objective of the present R&D is to develop a system for reducing wastes to half their

conventional volumes or less, by making effective use of waste soda or waste amine, which are

wastes produced by oil refineries in the same manner as excess sludge, which is the greatest

industrial waste produced by oil refineries in terms of volume. Technological development for

this system is a crucial issue both in terms of reducing the volume of industrial waste and

lowering environmental costs for oil refineries.

(1) Of oil refinery wastes, the volume of excess sludge produced is reportedly about 100,000

tons/year. A huge drop in dissolution work can be realized by reducing this volume by

one-half.

(2) The most common method of treating excess sludge has been to incinerate it after

dehydration. But revisions of the law governing waste treatment and cleaning (Waste

Management and Public Cleansing Law) have toughened regulations on CO and dioxin so

that more and more incinerators are being shut down and restrictions on incineration have

been multiplying.

(3) In addition to the increase in restrictions on the aforesaid modes of treatment, the costs of

such treatment have been skyrocketing.

(4) What is more, if sludge dissolution can be achieved by using waste soda, waste amine,

waste acid or waste heat, the wastes of oil refineries, reductions both in the volumes of

waste and in costs can be expected.

2. R&D Contents

This fiscal year, a small-scale sludge dissolution unit was fabricated after investigating methods

for solubilization of sludge using waste soda, waste amine and waste acid and after

investigating the effect on treated water properties when sludge treatment fluid has been

returned to an activated sludge unit. With this small-scale sludge dissolution unit, solubilization

rate, sludge reduction performance and treated water properties were investigated, and based

on the findings thereof, a unit for practical application testing was designed and preliminary

evaluations were begun.

2.1 Investigation of Excess Sludge Solubilization Method

Methods employing waste soda, waste amine and waste acid were evaluated, as were

combinations of these methods with physical destruction methods known up to the present. Use

of waste heat was also investigated.

2

2.2 Effect of Solubilization on Treated Water Properties

After investigating analytical methods and the properties of solubilization treatment fluid as

mentioned above, the effect on treated water properties when the solubilization treatment fluid

was returned to activated sludge unit was evaluated.

2.3 Evaluation of Sludge Reduction Performance by Small-scale Sludge Dissolution

System for Laboratory

A small-scale sludge dissolution unit was fabricated and its effect on solubilization rate, sludge

reduction performance and treated water properties was evaluated.

2.4 Design of Unit for Practical Application Testing and Preliminary Evaluations

Based on results obtained from the aforementioned, a unit for practical application testing was

designed and preliminary evaluations were begun on the assumption of treatment of waste

water from a practical oil refinery.

3. R&D Results

3.1 Evaluation of Excess Sludge Solubilization Method

3.1.1 Sludge Solubilization by Chemical Agents

(1) Effect of chemical agent types

The sludge solubilization performances of model agents of waste soda, waste amine and

waste acid from oil refineries were checked. The results appear in Figure-1. It was

confirmed that sludge solubilization is possible with all the test agents under investigation.

It was also noted that of these agents, the model agent for waste soda achieves a high rate

of sludge solubilization.

What is more, a comparative investigation was made of sludge solubilization performance

by representative model agents of waste soda and waste amine. The results are given in

Figure-2. It was found that sludge solubilization is possible with all the waste soda model

agents. Of these agents, model agent A, in particular, comes closest to realizing the sludge

solubilization performance of waste soda. It was found to have a high sludge solubilization

rate.

(2) Effect of chemical agent concentration

The effect of the concentration of model agent A was investigated. The results appear in

Figure-3. Sludge solubilization advances when the concentration of this agent is low, but

the rate of solubilization escalates as the concentration of test agent A is increased. This

agrees with the finding that a large volume of sludge solubilization can be obtained with an

extremely low concentration of soda (medium concentration or lower).

(3) Effect of temperature

The effect of the temperature of model agent A was also investigated, and the results

appear in Figure-4. Sludge solubilization advances when the temperature is high, and it

was found that a sludge solubilization rate of 50 mass% can be realized by treatment for

about 3 hours at around 60°C.

3

Slu

dg

e s

olu

bili

zatio

n r

ate

(m

ass%

)

Treatment period (h) Waste acid model agent Blank S

lud

ge

so

lub

ilizatio

n r

ate

(m

ass%

)

Treatment period (h)

Model agent B

Blank

Waste soda model agent Waste amine model agent

Model agent A

Waste soda

Model agent B

Figure-1: Sludge Solubilization by

Model Agent

Figure-2: Comparison of Waste Soda and

Model Agent

Slu

dg

e s

olu

bili

zatio

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(m

ass%

)

Treatment period (min)

Blank Low concentration

Medium concentration

Highconcentration

Slu

dg

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bili

zatio

n r

ate

(m

ass%

)


Figure-3: Effect of Agent Concentration Figure-4: Effect of Temperature

3.1.2 Sludge Solubilization by Oil Refinery Waste Heat (Low-temperature Waste Heat)

Since it was confirmed that temperature acts to promote sludge solubilization, an investigation

was made of solubilization by heating treatment alone, in consideration of the use of oil refinery

waste heat (low-temperature waste heat). The results are given in Figure-5. With heat treatment

alone at 60°C or below, sludge solubilization performance was low and the solubilization rate

was inadequate.

Next, solubilization through heat treatment (60°C) was applied so as to investigate the

possibilities for lowering agent concentration. The results appear in Figure-6. For heat treatment

at 60°C, a certain degree of agent concentration is necessary, and in order to attain a high

sludge solubilization rate of 40 mass% or more, it was found that agent of medium

concentration must be added and that the treatment duration must be prolonged to 3 hours or

longer.

4

Slu

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tio

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(m

ass%

)


Slu

dg

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bili

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tio

n r

ate

(m

ass%

)


Low concentration


High concentration

Figure-5: Heat Treatment Figure-6: Combined Treatment by

Heating and by Chemical Agent

3.1.3 Sludge Solubilization by Physical Destruction Treatment

(1) Sludge solubilization by physical destruction and chemical agent

An investigation was made of physical destruction treatment for the purpose of accelerating

the speed of sludge solubilization. A known sludge mill was used in the physical destruction

process. Figure-7 gives the results. In physical destruction treatment alone, the sludge

solubilization rate is low in comparison to chemical agent treatment using the waste soda

model agent A, but when physical destruction and chemical agent treatment are combined,

we find that the sludge solubilization rate and sludge solubilization speed both escalate

increase dramatically as compared to treatment by chemical agent alone.

(2) Changes in sludge floc diameter due to physical destruction treatment

In order to investigate the reasons that sludge solubilization is promoted by the physical

destruction process, the temporal changes in sludge floc diameter produced by sludge mill

were checked. Results appear in Figure-8. The sludge mill produced a sharp drop in sludge

floc diameter within the short time period of just a few minutes. In this way, it is believed

that sludge flocs are refined by the shear force of the sludge mill, which in turn causes the

rate of contact with the chemical agent to increase so that the sludge solubilization rate

escalates in a short time period.

Slu

dg

e s

olu

bili

za

tio

n r

ate

(m

ass%

)


Chemical agent treatment

Slu

dg

e f

loc s

ize

-mo

de

(u

m)

Treatment period (min) Physical destruction treatment

Physical destruction + Chemical agent treatment Sludge mill Low-speed agitator

Figure-7: Combined Treatment by

Physical Destruction and

Chemical Agent

Figure-8: Changes in Sludge Floc

Diameter due to Physical

Destruction Treatment

5

(3) Effect of each factor (agent concentration · temperature) in combined treatment

Figure-9 presents the results of an investigation into the effect of agent concentration,

using waste soda model agent A.

Slu

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(m

ass%

)


Blank Low concentration


Highconcentration

Slu

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(m

ass%

)


Figure-9: Effect of Agent Concentration

in Combined Treatment

Figure-10: Effect of Temperature in

Combined Treatment

With agent in the range of medium concentration, a high sludge solubilization rate of 40

mass% or more could be attained in the short time period of within 60 minutes. Findings on

the effect of temperature are presented in Figure-10. At a temperature of about 40°C, a

very high sludge solubilization rate of 50% or more could be reached within 60 minutes.

(4) Sludge solubilization by oil refinery wastes

Respecting combined treatment by physical destruction and chemical agent, a comparative

investigation was made of sludge solubilization performance using model agents of waste

soda, waste amine and waste acid discharged from oil refineries. Figure-11 shows the

results. By implementing physical destruction treatment with a sludge mill, an improvement

in sludge solubilization rate was anticipated when a model agent for waste amine and

waste acid was used, but this rate was low by about 25%.

In addition, an investigation was made of sludge solubilization using waste soda having the

typical constituents and composition of oil refinery waste soda. Figure-12 gives the results.

It was discovered that with waste soda, as in the case of model agent, a sludge

solubilization rate of about 40% could be attained within the short time period of about 60

minutes.

Slu

dg

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olu

bili

za

tio

n r

ate

(m

ass%

)


Waste soda (model agent)

Waste acid (model agent)

Waste amine(model agent)

Waste soda Model agent A

Slu

dg

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olu

bili

za

tio

n r

ate

(m

ass%

)


Figure-11: Sludge Solubilization by

Model Agent of Refinery

Waste

Figure-12: Comparison of Waste Soda and

Model Agent A

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3.2 Effect of Solubilization on Waste Water Properties

3.2.1 Evaluation of Sludge Solubilization Fluid Constituents

(1) Properties of sludge solubilization fluid

In order to investigate the effect on treated water properties when sludge solubilization fluid

has been returned to activated sludge unit, total organic carbon (TOC), nitrogen and

phosphorous contents were analyzed as properties of sludge solubilization fluid, and the

relationship between sludge solubilization rate and the concentration of each of these

constituents was determined. The results appear in Figure-13. There is a high correlation

between sludge solubilization rate and the concentration of each constituent in sludge

solubilization fluid, and it is suspected that as the sludge solubilization rate becomes higher,

it promotes the discharge and decomposition of each constituent from microbial cells

destroyed by solubilization.

Via

ble

ce

ll n

um

be

r (C

FU

/ml)

Sludge solubilization rate

Viable cell number (CFU/ml)

Sludge solubilization rate

Blank

Figure-13: Properties of Sludge

Solubilization Fluid

Figure-14: Microorganisms in Sludge

Solubilization Fluid

(2) Microorganisms in sludge solubilization fluid

In order to investigate the effect on treated water properties when sludge solubilization fluid

has been returned to activated sludge unit, an analysis was made of the quantities of

microorganisms in sludge solubilization fluid and the relationship between sludge

solubilization rate and the quantities of microorganisms was determined. The results

appear in Figure-14. There is a correlation between sludge solubilization rate and the

quantity of microorganisms in sludge solubilization fluid, and it was discovered that as the

sludge solubilization rate becomes higher, the quantity of microorganism declines

logarithmically. It was also discovered that solubility treatment does not destroy all the

microorganisms in sludge.

3.2.2 Properties of Sludge Solubilization Fluid Using Oil Refinery Wastes

Respecting combined treatment by physical destruction and chemical agent, an investigation

was made of sludge solubilization performance using model agents in imitation of waste soda,

waste amine and waste acid discharged from oil refineries. Figure-15 presents the results of

properties analysis of COD, nitrogen and phosphorous contents in each sludge solubilization

fluid obtained from the investigations.

7

It was found that since the model agent for waste soda exhibits the highest sludge solubilization

performance, COD also becomes high. On the other hand, because the sludge solubilization

performance of agent for waste acid is low, the concentration of each constituent also became

low. With the model agent for waste amine, COD and nitrogen contents were high even though

sludge solubilization performance was low. This can be ascribed to the fact that amine itself

contains the element nitrogen, plus the fact that it is a compound of high COD.

CO

D in

so

lub

iliza

tio

n f

luid

(m

g/l)

Waste soda (model agent)

Waste acid (model agent)

Waste amine (model agent)

Waste soda(model agent)

Waste amine (model agent)

T-N

an

d T

-P in

solu

bili

za

tio

n f

luid

(m

g/l)

Waste acid (model agent))

Figure-15: Properties of Solubilization Fluid Using Oil Refinery Wastes

Figure-16 presents the results of properties analysis of COD, nitrogen and phosphorous

contents in sludge solubilization fluid using the model agent for waste soda, which exhibits the

highest sludge solubilization performance, and in sludge solubilization fluid using typical waste

soda. It was disclosed that the sludge solubilization fluid by waste soda treatment contains a

high COD content as compared to the fluid by other model agent. This is ascribed to the COD

constituent inherently present in waste soda.

CO

D in

so

lub

iliza

tio

n f

luid

(m

g/l)

Waste soda

T-N

an

d T

-P in

so

lub

iliza

tio

n f

luid

(m

g/l)

Model agent A

Waste soda

Model agent A

Figure-16: Comparison of Solubilization Fluid Properties

by Waste Soda and Model Agent

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3.3 Evaluation of Sludge Reduction Performance by Small-Scale Sludge Dissolution

Unit

3.3.1 Fabrication of Small-scale Solubilization Unit

A small-scale solubilization unit that can be attached to a 40L small-scale activated sludge unit

was designed and fabricated. The unit automatically recovers excess sludge generated by the

40L small-scale activated sludge unit, subjects it to solubilization, and returns it to an aeration

tank.

3.3.2 Test of Sludge Reduction by Small-scale Solubilization Unit

In order to check the solubilization capacity of the newly-fabricated solubilization unit,

solubilization tests were performed by treating 1 liter of sludge at a MLSS (mixed liquor

suspended solids) of 8,000 mg/L with chemical agents at high concentrations. Figure-17 depicts

the temporal change in solubilization rate by mill unit operating period. In automatic sludge

solubilization by the small-scale solubilization unit, the unit operated in accordance with a

control program and solubilization treatment was possible. In one hour, the solubilization rate

reached about 40%, and it was confirmed that the unit has adequate performance for use as an

automatic sludge dissolution system attached to small-scale activated sludge unit.

Sludge before and after solubilization treatment by the unit was observed under microscope.

Sludge micrographs (low magnification) appear in Figure-18. It was observed that in sludge that

had formed floc prior to treatment, not only was the floc destroyed after treatment, but the

so-called residue was also uniformly dispersed.

Slu

dg

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bili

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tio

n r

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(m

ass%

)

Small-scale solubilization unit


Batch-type mill

Figure-17: Temporal Changes in Solubilization Rate

Figure-18: Sluge Photos Before Solubilization (left),

After Solubilization (right)

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3.3.3 Evaluation of Sludge Reduction Performance by Small-scale Activated Sludge Unit

Sludge dissolution tests were performed in which excess sludge discharged from a 40L

small-scale activated sludge unit that was running under refinery activated-sludge-unit operating

conditions underwent solubilization and was returned to the activated sludge unit for the

purpose of achieving a 50% sludge reduction rate. The amount of sludge that underwent

solubilization was the same as the amount of sludge discharged from an activated sludge unit

during normal operation.

Table-1 gives the temperature, pH, MLSS and MLVSS/MLSS for each test category. Each value

is given as the average of values from one month after the start of testing up to test completion.

(The same is true of all measurements hereafter.)

In sludge dissolution, sludge (alkaline) undergoing solubilization by chemical agent and mill was

returned to the aeration tank but no significant changes in pH could be observed. There

appears to be no effect when the amount of sludge treated is the same as the amount

discharged during normal operations. The amount of organic substances (MLVSS/MLSS) in

sludge was observed to trend downward slightly in the 37°C test category.

In all test categories, the volume of dissolved oxygen (DO) was upheld at 4 ppm or more

throughout the test duration, and although SV30 trended at close to 100, active sludge

treatment operations could be maintained without bulking by using both coagulant and sludge

sedimentation improver.

Table-1: Temperature, pH, MLSS, MLVSS/MLSS during Sludge Solubilization

Operations

Temperature

(measured value)

pH MLSS MLVSS/

MLSS

Test category a; 30°C 30.3 7.3 2300 0.91

Test category b; 37°C 37.0 7.5 1950 0.85

Normal operation (30°C) 30.4 7.4 2000 0.90

Next, from an analysis of treated water properties, the volume of chemical oxygen demand

(COD) is given in Figure-19; total nitrogen (T-N) appears in Figure-20, and total phosphorous is

indicated in Figure-21. In each of the figures, the results of normal operation and of dissolution

operation are presented on the horizontal axis. In COD measurements, although the COD

withdrawal rate is shown as 95% or more in all test categories, a slight rise was confirmed in the

COD value of treated water in the 30°C test category. In measurements of T-N and T-P also, a

slight rise in the value of T-N in treated water was observed.

Figure-22 gives the mean values of sludge reduction rate in sludge dissolution tests by

small-scale activated sludge unit conducted from two weeks after the start of testing over a

100-day testing period. A volume of sludge equal to the volume discharged in normal operations

at 30°C and 37°C was dissolved at a solubilization rate of 40% or more, and after continuing

with sludge dissolution, the sludge reduction rate could be stabilized at 50% with no drop in

sludge reduction performance for one month or longer.

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Wa

ste

wa

ter

CO

D

Wa

ste

wa

ter

CO

D

Tre

ate

d w

ate

r C

OD

Tre

ate

d w

ate

r C

OD

Dissolution operationNormal operation Dissolution operation Normal operation

Figure-19: COD Value in Waste Water and in Treated Water

(30°C; left, 37°C; right)

Dissolution operationNormal operation Dissolution operation Normal operation

Figure-20: T-N Value in Waste Water and in Treated Water


S

lud

ge

red

uctio

n r

ate

(%

)

Dissolution operation

Normal operation

Dissolution operation

Normal operation

37°C operation 30°C operation0

Figure-21: T-P Value in Waste Water and

in Treated Water


Figure-22: Sludge Reduction Rate in

Dissolution Operations

3.4 Design of Unit for Practical Application Testing and Preliminary Evaluations

3.4.1 Design of Unit for Practical Application Testing

Making full use of laboratory test findings and the results of prior evaluation tests on practical

equipment designs (sludge mill, sludge thickener), a unit for testing practical applications was

designed. A photo of the unit for testing practical applications appears in Figure-23. Figure-24

presents a concept diagram of the sludge thickening and recovery process.

11

Sludge solubilization

tank Chemical agent

tank

Solubilization fluid pump

Sludge mill

Chemical agent injection pump

Sludge coagulant

Supply sludge

Anions

Cations

Heating steam

Inlet hopper

Thickener (rotary component)

Wastewatersludge

Figure-23: Unit for Practical Application

Testing

Figure-24: Sludge Thickening/Recovery

Process Diagram

3.4.2 Unit for Practical Application Testing and Preliminary Evaluations

(1) Sludge solubilization test

Batch tests of sludge solubilization were conducted using unit for practical applications

testing. Used as the chemical agent was the model agent for waste soda, since it was

discovered from investigation of the conditions for excess sludge solubilization in laboratory

that this agent exhibits a high sludge solubilization performance. The findings of an

investigation into the effect of chemical concentrations are presented in Figure-25.

Figure-26 presents the results of investigation into the effect of sludge mill rotary speed.

Sludge solubilization performance equivalent to that of laboratory test results was

confirmed.

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High speed Medium speed Low speed Low concentration


High concentration

Slu

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Figure-25: Effect of Agent Concentration Figure-26: Effect of Sludge Mill Speed

From an analysis of the properties of sludge solubilization fluid, it was confirmed that

properties are the same as in solubilization fluid during laboratory tests.

(2) Sludge thickening/recovery tests

Batch tests were conducted on sludge thickening/recovery using sludge thickener and

sludge recovery unit. Table-2 presents the results. It was found that the presence or

absence of heating, for instance, or the rpms has a profound effect on the percentage of

water included in sludge. It was possible to recover sludge with water content stabilized at

the low percentage of 70%, the same as the percentage found in preliminary tests of

sludge thickener, undertaken for design of practical equipment.

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Table-2: Sludge Thickening/Recovery Test Results with Unit for

Practical Application Testing

Test No. 1 2 3 4 5 6

Sludge treatment volume (m3/h) 3.0 2.0 3.0 4.0 3.0 3.0

rpms (rpm) 0.09 0.06 0.09 0.12 0.09 0.09

Sludge coagulant volume cations (%) 1.20 1.20 1.20 1.20 0.84 1.56

anions (%) 0.40 0.40 0.40 0.40 0.28 0.52

Presence/absence of heating Absent Present Present Present Present Present

Water percentage in sludge (wt%) 83 69 75 77 75 74

4. Synopsis

4.1 R&D Results

4.1.1 Investigation of Solubilization Method for Excess Sludge

Sludge solubilization methods were investigated using oil refinery wastes, namely, waste soda,

waste amine and waste acid, and comparisons were made with caustic soda so as to determine

characteristics. An investigation was also made using model agents of waste soda, waste amine

and waste acid, and it was found that the model agent for waste soda exhibits the highest

sludge solubilization performance. In addition, treatment was performed in combination with

physical destruction, and a high sludge solubilization rate could be attained in a shorter time. It

was also confirmed that waste soda having the typical composition and constituents of oil

refinery waste soda yields the same sludge solubilization performance as model agent.

4.1.2 Effect of Solubilization on Treated Water Properties

Through analysis of the properties of sludge solubilization fluid, the effect on treated water

properties when sludge solubilization fluid has been returned to activated sludge unit was

checked. As the sludge solubilization rate escalated, the concentrations of COD, T-N and T-P in

sludge solubilization fluid also became higher. From a comparison of the constituent properties

of COD, nitrogen and phophorous in sludge solubilization fluid using a typical waste soda, as

opposed to sludge solubilization fluid using caustic soda, it was discovered that the COD

content was higher in sludge solubilization fluid resulting from waste soda treatment than in

comparable fluid from caustic soda treatment.

4.1.3 Sludge Reduction Performance by Small-scale Sludge Dissolution Unit

A small-scale system with solubilization unit attached to small-scale, active sludge unit was

fabricated, and evaluations were made of solubilization rate, sludge reduction performance and

treated water properties. Using caustic soda, sludge solubilization was carried out in batch-type

laboratory units and sludge dissolution was performed. Over a one-month period, sludge

reduction of nearly 50% was achieved. As for the effect on treated water properties, on the

other hand, a slight rise in COD (Mn) was confirmed.

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4.1.4 Design of Unit for Practical Application Testing and Preliminary Evaluations

A unit for testing practical applications was designed, based on laboratory test results, and

preliminary evaluations were begun on the assumption that actual waste water from oil

refineries is being treated. A unit for testing practical applications was designed based on

detailed operational data obtained on extant activated sludge units, and on prior evaluative tests

of sludge mill and sludge thickener. Preliminary evaluations, including sludge solubilization tests

and sludge thickening/recovery tests, were made for the sake of long-term practical application

tests to be conducted in the next fiscal year. Performance equivalent to that of laboratory test

results and prior evaluation test results was confirmed.

4.2 Future Issues

4.2.1 Investigation of Solubilization Method for Excess Sludge

From an investigation of sludge solubilization by model agent in imitation of refinery wastes, it

was confirmed that sludge solubilization performance is equally high with waste soda and with

caustic soda. The COD (Mn) content in sludge solubilization fluid from using waste soda is

higher than that in comparable fluid from using caustic soda. In the future, investigations should

be made on the use of waste soda as the chemical agent in sludge solubilization.

4.2.2 Investigation of Sludge Reduction Performance by Unit for Practical Application

Testing

In laboratory tests using refinery wastewater, a sludge reduction performance of nearly 50%

was achieved. In considering effect on treated water properties, however, it was also discovered

that there is a slight rise in COD (Mn). In the future, investigations should be made of

solubilization treatment conditions, of sludge reduction performance and of trends in treated

water properties under conditions of variable wastewater load and variable temperature, using

actual wastewater from refineries.

Copyright 2002 Petroleum Energy Center. All rights reserved.

Documents

Development of Oil Refinery Waste Reduction Technology