Mathematical Model of Recalcination of Lime Sludge with Fluidized Bed Reactors


            WATER POLLUTION CONTROL RESEARCH SERIES • ORD 17090EHQ 09/70
                   MATHEMATICAL MODEL OF
                RECALCINATION OF  LIME SLUDGE
                WITH FLUIDIZEO BED REACTORS
U.S. DEPARTMENT OP THE INTERIOR • FEDERAL WATER QUALITY ADMINISTRATION

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        WATER POLLUTION CONTROL RESEARCH SERIES
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MATHEMATICAL MODEL OF RECALCINATION OF LIME
SLUDGE WITH FLUIDIZED BED REACTORS
by
G. J. Ducar
P. Levin
General American Transportation Corporation
Niles, Illinois 60648
for the

FEDERAL WATER QUALITY ADMINISTRATION

DEPARTMENT OF THE INTERIOR
Program #17090 EHQ
Contract #14-12-415
FWQA Project Officer, R. Smith
Advanced Waste Treatment Research Laboratory
Cincinnati, Ohio
September, 1970
! IPPApV
(L« •_ I '.. l'I '. 3
•')-•;;. of ths Iniubf.
..';j-,
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FWQA Review Notice
This report has been reviewed by the Federal
Water Quality Administration and approved for
publication. Approval does not signify that
the contents necessarily reflect the views
and policies of the Federal Water Quality
Administration, nor does mention of trade
names or commercial products constitute
endorsement or recommendation for use.
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ACKNOWLEDGMENT

We wish to express our appreciation to the following people for their

fine cooperation in assembling data for this project:

Jim Amertnan, Ann Arbor Municipal Water Plant

Lee Bingham, P. H. Glatfelter Company, Pennsylvania

John Moran, Phillip Hinkley, S. D. Warren Paper Company, Muskegon, Michigan

Jim Kuehl, Kimberly Clark, Neenah, Wisconsin

Walter McMichael, FWQA, Cincinnati, Ohio
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TABLE OF CONTENTS

PAGE MO.

ACKNOWLEDGMENT i

ABSTRACT iv

INTRODUCTION 1

Origin of Lime Sludges 2

DESCRIPTION OF SYSTEMS ANALYZED 3

Terminology 3

System Components and Operation 3

Method of Approach 8

RESULTS 10

Data Collected 10

Equations Developed 10

Sizing the Reactor 13

System Electrical Power 23

Lime Loss Rates 23

Ash 25

Reactor Heat Balance 26

Systems Costs 26

Electrical 26

Fuel 2?

Operating and Maintenance 27

Makeup Lime and Solids Disposal 28

Equipment Capital Costs 29

Installation and Consulting Fees 29
ii
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TABLE OF CONTENTS (CONT'D)

PAGE NO.

Total Cost of Maintenance and Operation 31

COMPUTER PROGRAM 32

Listing of Program 32

Flow Chart 32

How to Use Program 36

Operation 36

Reactor Sizing Limit 36

CONSLUSIOWS AND RECOMMENDATIONS Ul

Performance of the System Ifl

Factors to be Considered U2

Equipment Design ^3

BIBLIOGRAPHY 1+3

TERMINOLOGY 1+6
ill
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ABSTRACT

This report describes the development of a computer program to evaluate

lime sludge recalcination systems. Data for the program was collected from

a literature survey and field trips to operating installations of pulp mills

and a water softening plant.

Some of the design relationships were found to have the same correlating

variables for the recalciner as for the fluidized bed incinerators. Equations

were developed for the least square curves which fitted the data best. These

equations were used as the basis for the computer program developed to size

some of the major components and to estimate capital, operating and maintenance

costs for fluidized bed lime recalcination systems.

The fluidized bed reactor recalcining process has not yet been installed

at any sewage treatment plant. Therefore, no data on the process was available.

However, the pulp and paper plants and water softening plants presently recalcine

in a manner which would be applicable to tertiary treatment recalcination

requirements. Therefore the models developed herein represent the recalcination

process as applied to tertiary treatment plants.

The computer program developed will be used (by FWQA) as a subroutine for

the executive computer program entitled "Preliminary Design of Wastewater

Treatment Systems." The executive program will be used to evaluate and optimize

new wastewater treatment systems which are to be funded by FWQA.

This report was submitted in fulfillment of Contract #14-12-415, Program

#17090 EHQ, between the Federal Water Quality Administration and General

American Transportation Corporation.
iv
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INTRODUCTION

Lime (calcium hydroxide, Ca(OH)p) is extensively used in "both water and

waste treatment processes. In combination with soda ash, it is used to

reduce the hardness of water. Present indications are that it can he used

economically to reduce the nitrogen and phosphorus content of wastewater.

The disposal of lime sludges produced in these water and wastewater

treatment processes is "becoming a serious problem due to the limited capacity

of our environment to absorb such wastes. These sludges, once considered

innocuous, now are considered as pollutants adversely affecting the environ-

ment. The requirements for higher degrees of treatment will require increased

quantities of lime at wastewater treatment plants, presenting increased disposal

problems for the increasing volumes of sludges produced.

The most ideal solution available for disposal of this sludge is to

convert it economically into a usable product. This can readily be accom-

plished by heating it to about 1600°F and decomposing the sludge to calcium

oxide and rehydrating or slaking the calcium oxide for recycling to the process.

This processing is commonly referred to as recalcining.

Various types of reactors are available to accomplish this, including

rotary kilns, multiple hearth and fluidized bed incinerators.

The purpose of this program was to develop a mathematical model of a

fluidized bed reactor for recalcining calcium carbonate sludge. The model

is composed of equations which represent the calcination equipment and

process. This model should be of assistance to FWPCA in sizing reaction
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vessels and related equipment, the amount of fuel and power required, and

estimates of the capital, operating, and maintenance costs for fluidized

ted reactors used for lime recalcination. The necessary equations were

developed from data obtained from the literature and from field surveys of

plants which recalcine calcium carbonate produced in the manufacture of wood

pulp and the lime-soda ash water softening process. No plants are currently

in operation which recalcirie lime from primary or tertiary treatment processes

in sewage treatment plants. These systems closely resemble the equipment which

could be used in sewage treatment applications in the near future.

Origin of Lime Sludges

The addition of lime to raw sewage or secondary effluents is an effective

procedure for reducing phosphorus concentrations. The residual dissolved

phosphate level declines as a function of the pH to which the wastewater

is treated, with about 0.15 mg/1 P remaining at a pH of 11. The elevation

to pH 11 also results in conversion of the NH. to NH,. which can be removed

in an air stripping tower. The sludge precipitated either in the primary

tank or tertiary plant contains calcium carbonate sludge with both organic

and chemical impurities.

Similarly, in a typical water softening process, sufficient lime is added

P
to elevate the pH to 11 and precipitate the Mg(OH) and CaC0 .

Subsequent recarbonation of the effluent or softened water at a pH of

11 depresses the pH to approximately pH 9-5, precipitating an essentially

pure (9S$O CaC0_ which can be effectively recalcined.
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DESCRIPTION OF SYSTEMS ANALYZED

Terminology

A schematic of the reactor or combustion chamber, which is the heart of the

fluidized bed recalcining system, is shown in Figure 1. The parameters related

directly to the reactor are shown and the various regions of the reactor are

labeled on Figure 1. The lower section of the reactor consists of a fluidized

air plenum, an air distribution grid and a pellet cooling section called the

cooler. The center section of the reactor is the calcining section containing

the fluidized Ca0 pellet bed. Above the calcining section is the freeboard. The

terminology shown on Figure 1 is specifically related to the reactor vessel. How-

ever, auxiliary equipment was considered on this program. Therefore additional

terminology was required and this terminology is given in Appendix A.

System Components and Operation

The system components included in this study are shown in Figure 2. The

recalcined lime handling system (not shown in Figure 2) and the components shown

in Figure 2 are included in the capital costs developed on this program. The

layout shown is the complete fluidized bed recalcining system which is usually

purchased as a package. This system was used as the basis for including

equipment in the study because cost data collected included all of the components

shown in Figure 2 plus the lime handling system. Since it was not possible to

obtain costs for the individual components it was necessary to develop cost

information for the total system. The costs developed on this program do not

include land costs for recalcining equipment or ash disposal or land costs for

storage of wasted CaC0~ for a non-recalcining installation. Slaking lime loss

rates were not included in this program.
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To Stack
Calcining
Zone
Sludge
Feed

Cooler
Plenum
'Fluidizing Air
Figure 1 RMCTOR TERMINOLOGY
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To Stack (to atmosphere)
T Exhaust Fan
Water
Fluidized
Beds
(Pellets)
Calciner
Feed( Powder)
Sludge
Cooling Compartment

, Fuel (Gas or Oil)
Pelletized
Lime & Waste
Handling System
Fluidizing Air Blower
Figure 2 SCHEMATIC OF RECALCULATION SYSTEM
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Calcining Process Description

Since no primary or tertiary lime recalcinat ion- sludge combustion

systems were in operation at the time of this report the process was not

available for analysis. However, the pulp and paper and water softening

recalcining processes closely resemble the tertiary and primary recalcining

process which could be used in the future. The calcium carbonate sludge is

initially dewatered either by a centrifuge or vacuum filter to a cake with a

solid content of 60 to 65 percent. This cake is then passed through a mixer

and cage mill where it is mixed with dried recycle CaC0_ and hot stack gases

containing fine CaC0_ particles. The stack gases are usually diluted with air

or quenched with water to reduce the gas temperature entering the cage mill to

a level which will not affect the cage mill. The mixture is ground and dried

in the cage mill and the particulate matter is carried with the gases to the

primary cyclone.

Very fine material CaC0_ passes through the primary cyclone to the

secondary cyclone. The large particles are either sent to the reactor and

mixed with soda ash for recalcination and particle growth or recycled through

the cage mill (75% are recycled). The finer particles entering the secondary

cyclone pass through and are collected in the scrubber. The heavier particles

entering the secondary cyclone are sent to the feed bin and then to the reactor

for recalcination or particle growth.
Soda ash is added to the feed stream to promote pelletization of

particles in the reactor. It is a necessary additive which melts to a sticky

material in the reactor and coats the surface of Ca0 particles causing them to
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stick together. The cost of soda ash is $33/ton (19^9 price less freight)

and the normal feed rate for pulp and paper plants is approximately 0.5 to

1.0$ by weight of the sludge leaving the devatering device.

The dried CaC0 sludge is fed into the fluidized Ca0 "bed in the calcining

section of the reactor with fuel to make the endothermic reaction proceed. The

material remains in the reactor at a temperature of approximately l620°F. (recal-

cination occurs at approximately 1520°F.) until it is "blown up and out through

the freeboard zone by the fluidizing gases (fine particles) or it falls through

a pneumatic level sensitive valve into the cooler zone. The freeboard zone

prevents larger particles from leaving the reactor with the exhaust bases. The

particles which have grown to pellet size, from continued agglomeration accel-

erated by the soda ash, enter the cooler section at l620°F. and are cooled to

approximately ^00°F. by the fluidizing air which passes up through the cooler.

The fluidizing air is preheated to approximately 400°F. in the cooler.

The pelletized lime is removed from the cooler through a pneumatic level

control valve. The lime is pelletized because it is more convenient to handle

in a pellet form, rather than a powder. Also, since the particles forming the

pellet, for the most part, are recycled through the reactor several times more

complete recalcination is assured than if the finer particles were used as the

final product. For proper fluidication in the recalcining section a particular

particle size range must be maintained.

Since the Ca0 particles continually grow in the reactor it is necessary to

replenish the fine particle supply in the reactor periodically. This is done

by crushing some of the stored pelletized lime and feeding it to the reactor.
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This particle addition is also necessary when the recalcining section becomes

loaded with impurities which must be dumped to waste.

The input stream to be used for the computer program developed is the

feed material CaC0-, in a dry (zero water content) state. This is equivalent

to the composition of the material leaving the cage mill in a dried state.

All of the water in the feed is evaporated in the cage mill by the hot exhaust

gases.

Method of Approach

The method of approach used for this study was to:

l) Review the literature to establish the availability of published

data concerning recalcination by fluidized bed reactors;

2) Visit representative pulp mills and water softening plants to

obtain data on fluidized bed reactors in use today;

3) Develop a computerized procedure for evaluating lime sludge

recalcination systems assuming the systems at the pulp mills

and water softening plants closely resemble the equipment which

could be used in future sewage treatment applications.

E&r necessity, the evaluation procedures are limited in their application

to the range of the parameters disclosed by the literature search and facility

visits. Also, the available funding limited the amount of facility visits.

The facility visits were conducted at:

1) A pulp mill of Kimberly-dark at Reading, California which was not

visited directly, but data on it were obtained by a personal visit

to the corporate engineering offices located in Neenah, Wisconsin,

8
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2) A water softening plant at Ann Arbor, Michigan,

3) A pulp mill of P. H. GLattfelter at Spring Grove, Pennsylvania,

k) A pulp mill of S. D. Warren Company at Muskegon, Michigan, and

5) A water softening plant at Lansing, Michigan.

A review of the literature found no recalcination units treating sludge

from wastewater treatment plants. There were recalcination units utilized

to recalcine CaCjZ^ sludge produced in the manufacture of wood pulp and the

lime-soda ash water softening process.

One commercial process which reportedly employs addition of lime to the

primary tank suggested that this lime can be recovered by dewatering and

incinerating the primary sludge and slaking the resulting ash to recover

the lime; however, our literature study did not reveal any such plants even

in the design stage. We were also unable to find any plants calcining sludge

containing calcium phosphate. The recalcination of this material would result

in a build-up of non-volatile impurities in the Cafi produced.

In this study, considerable data were obtained in the recalcination of

essentially pure calcium carbonate by visiting paper plants which produce

this type of sludge. Our model is therefore based on the recalcination of

essentially pure Ca.C^. At present, this appears to be a realistic approach

since at the Advanced Waste Treatment Plant in operation at Blue Plains we

were advised that none of the lime produced from impure CaCj#~ was recycled

to the system. It was the operator's belief that this material would be

utilized more effectively as agricultural lime because of its phosphate

content. Only the essentially pure CaC0^ produced in the settling basin

following recarbonation would be recycled to the multiple hearth furnace

they were utilizing for recalcination.

9
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RESULTS

Data Collected

Table I is a summary of the data collected on the recalcination

systems studied during this program. This data was obtained by visits

to installations and a survey of literature. The costs presented in Table I

are the costs actually paid for the equipment. These costs can be com-

pared by applying a cost index relating purchase dates.

The equipment sizing and capital cost data are reliable since they

were obtained from visual inspection and available drawings. However, the

data for operating costs (fuel, power and operator), though fairly accurate,

were not readily available. The gross costs ($/ton of recalcined lime)

were available. These costs are functions of operating efficiencies which

were in various stages of improvement at the various plants. Note that there

is no reason that the fluidized bed calciner cannot be used in smaller sizes.

Since the plants surveyed were purchased at different times, a standard

cost reference date of February, 1968 was chosen for this program. All

local unit prices were corrected to the national average of February, 1968

prices, using the cost index of the Department of the Interior as found in

Engineering News Record magazine.

In Table I, Location U, the design capacity rating ^5/70 means that the

unit has a design capacity of either k5 or 70 TPD depending on the diameter

of the firebrick. The unit capacity can be upgraded to 70 TPD by removing

firebrick, thus increasing the bed diameter.

Equations Developed

Equations were developed based on data gathered from the field and several

useful publications. The data were plotted using various correlations and

least square curves were plotted. Equations were developed for the best

correlations found relating the variables.

10
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ITEM
Purchase Date
Startup Date
Design Tons Dry
Ca0/Day
% Ca0 in Reactor
Product
Fuel Type
Number of Sludge
Feed Points
Type of Feed

1
Kimberly
Clark
Jan 63
Oct 6k
50
88
Wo. 6 Fuel
Oil
9
Pneumatic
TABLE I
FIELD DATA

2
Ann Arbor,
Mich.
1965
Feb 67
2k
—
No. k Fuel
Oil
6
Pneumatic
LOCATION
3
P. H.
Glatfelter
Nov 65
Nov 66
128
85
No. 6 Fuel
Oil
2k
—

k
S. D.
Warren
Feb 63
Dec 63
i+5/70
85
No. 6 Fuel
Oil
12
Pneumatic

5
Lansing,
Mich.
1953
195^
30
88-91.5
No. 6 Fuel
Oil
_
_
10
Lime Recovered
% of Feed

Total System
Cost, $ $200,000

Number of Bed
Burners
Fluidizing Blower,
HP
Fluidizing Blower,
SCFM
Fluidizing Blower,
inches H?0
Bed Temperatures,
°F

Freeboard Tem-
peratures, °F

Sludge Feed Point
Distance above
Grid, ft 1.5-2
Cooler Section
Included No

Bed Warmup Time,
hrs 2k
90
$575,000
12
12
125
k790
19U
1600
1650
100
2100
19^
1580
1^95
200
3800
166
1600
1550
300
10, 000
-
1650
1600
1.5
Yes
Yes
Yes
8
90
8
Yes
11
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ITEM
TABLE I (COM"D)

FIELD DATA
LOCATION

3
Bed Cooling Rate

Major Problems
Inside Diameter
of Calcining
Section, ft

Inside Diameter
of Freeboard
Section, ft
Static Bed Depth,
ft

Expanded Bed Depth,
ft
Expanded Bed Free-
board, ft

Total Installed HP
30°F/hr
Slaking
8
25°F/hr
Slaking
Pellet trans-
fer to cooler.
Reactor scal-
ing
8/10
Pellet trans-
fer to cooler.
Reactor scal-
ing
11
1U
6
9.8
15
Ul6
8.5
6
9.0
16.5
3^5
16.5
7
10.5
16.7
U65
-
7
10.0
16.7
101+8
-
7
10.5
_
l+6o
12
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Sizing the Reactor

A recalcination system is rated on its output design capacity of Ca0.

For a given output design capacity (CAP), the total dry solids which must be

handled by the system is

PDS = CAP (2000.)/ (x)(y) (l)

Note that there are 2000. pounds per ton. The weight of Ca0 contained in one

pound of CaC0~ is termed x, and x = ^6/100 = 0.56. The weight of CaC0 con-

tained in one pound of dry solids entering the reactor is defined as y and

this must be determined for the particular sludge being recalcined. Field data

obtained were for systems as small as PDS = UOOO. Therefore, because of the

uncertainty of curves such as for 0HP and IHP, it was decided to limit the

lower limit of reliability of the data to PDS = lj-000. Similarly, since no

fluidized bed reactor was found with a bed grid diameter (DGC) in excess of

l6 feet (Kansas City fluidized bed incinerator), this was taken as the upper

limit of structural achievement using standard construction materials.*

Figure 3 shows a plot of the net heat "input to the reactor required in

excess of the endothermic heat of the CaC0 —*• Ca0 + C02 reaction.

To obtain the net heat input (QCA0 = Btu/ton Ca0), the endothermic heat

of the reaction (2.69 x 10 Btu/ton of Ca0) was subtracted from the total gross

heat input to the reactor (fuel, dried sludge and air preheat in cooler). The

result shown in Figure 3 is

QCA0 = 5-0 x 106 (2)

To obtain the total net heat input to the reactor, the net heat input per ton

of Ca0 is multiplied by the design Ca0 capacity of the reactor.

WMQN = QCA0 (CAP) (3)

*Dorr-Oliver has informed the authors that they have industrial calciner
units in operation with diameters of 45 feet.

13
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S 20

II
05
S )

§ 16
) 12

o
, !

X 10

',-!
0)
PP 8

o
! '

iCAtf
7) 5
V\2
V

™ - " • --1" ' •
= 5.0 x 106
\ L
\
\
>P

-- —

^i^I
i
!

;

1
n

nn-
ii

It 6 8 10 12 Ik 16 18 20 22 2h 26 28 3<
Pounds of Dry Solids/Hr x 10~3 = PDS
Figure 3 NET BTU/TON Ca)6 VS POUNDS DRY SOLIDS/HE
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Then similarly
END0 = 2.69 x 1C6 (CAP)
and the gross heat input to the reactor is

SUMQ = SUMQW + EMD0 (5)

It is possible that more than one reactor may be needed for a given

installation. This is because of the maximum sizing limit of l6 feet diameter

in the calcining grid section (DGC). When the required recalcining capacity

exceeds the capacity of a reactor with DGC = 16 feet more than one reactor

is required for the installation. This is handled by specifying a sufficient

number of reactors (ZIl) of equal calcining grid diameter (DGC), to handle

the required capacity. Thus the net heat input to each reactor is

SUMQI = SUMQN/ZII (6)

Each reactor handling SUMQI will have a calcining grid cross-sectional

area (Figure 4) of

AGC = SUM£[/2l4-l, 000 (7)

The diameter of the calcining grid is

DGC = [U.O (AGC)/7r] ^ (8)

with a maximum limit of DGC = 16.0 feet.

The pounds of dry solids per hour which must be handled by each reactor

in the system is

ZI = PDS/ZII (9)

Since the feed material enters the reactor dry, because of the evaporation

process in the cage mill, the reactor calcining section cross-sectional area

does not vary vertically as does the fludized bed incinerator handling wet
15
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30

26
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fit

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AGC-JI

lares (0,0
AGC = BTBUN/2Ul,OOOv

X
^x^
™

^X^

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= F-0.973 + 0.2^4
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20
30
hO
50
60
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100
Calcining Grid Cross-Sectional Area -• ft = AGC
Figure U DESIGN NET HEAT INPUT TO ffiD VS CALCINING GRID CROSS-SECTIONAL AREA
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sewage sludge. Therefore

DFC = DGC (10)

for the recalciner.

Figure 5 shows the relationship determined for the freeboard diameter

located above the cylindrical recalcining zone

DF0 = (DGC - i.5)/o.U9 (11)

The cross-sectional area of the freeboard zone is

AF0 = TT (DF0)2/U.O (12)

The fluidized bed in a recalciner is composed of Ca0 pellets too large

to be carried into the freeboard by the exhaust gases and too small to be

dropped into the cooler section.

The expanded volume (VE) of the fluidized bed in the recalcining zone

of each reactor is (Figure 6)

VE = SUMQN/23,700 (13)

where SUMQN is changed to SUMQI when more than one reactor is used in a system.

Note that the least squares fit curve was not used for this relationship but

a slightly modified parallel line was used passing through the origin (0,0).

This eliminated a negative net heat input at zero bed volume which is physically

unreasonable.

It has been found that the expanded fluidized bed volume in reactors is

about 50$ greater than the static bed volume so

VS = VE/1.5 (1*0

Field data obtained indicated an expanded bed depth (HE) of from 9 to

10.5 feet. Most of the data showed a bed depth of 10 feet

HE = 10.0 (15)
17
-------
I •
(.,
fDGC - 1.5 + — DF0
0
2 U 6 8 10 12 lU 16 18 20 22 2k 26

Inside Diameter in Freeboard above Calcining Section = DF0
Figure 5 INSIDE DIAMETER IN CALCINING SECTION VS INSIDE DIAMETER

IN FREEBOARD ABOVE CALCINING SECTION
-------
'
30

if.

16
I

-------
For 50$, bed expansion on fluidization the static bed depth is

HS = HE/1.5 (16)

The following physical dimensions vere estimated as

HEXP =0.5 ' (17)

HP = 3.0 (18)

The height of the cooler section (HC) did not vary significantly with unit

capacity and the relation

HC = 8.5 (19)

was found to approximate most of the data.

Figure 7 shows the freeboard height to be closely approximated by

HF = 16 (20)

Summing the heights of the individual sections of the reactor, the

overall reactor height can be closely approximated by

0RH = HP + HC + HE + 0.5 + HF + HEXP (21)

Note that the 0.5 feet added to the 0RH term represents the approximate

distance between the height of the expanded fludized bed (HE) and the

beginning of the transition section between the recalcining and freeboard

zones.

Figure 8 shows the relationship between the number of feed points in

the reactor and the design dry solids feed rate to be

NFP = 2.3 + 0.00087 (PDS) (22)

where PDS is changed to ZI when more than one reactor is required in the

system. This number must obviously be rounded-off to the nearest integer

value.
20
-------
I,,
;
4567 9 10
Expanded Bed Depth, ft = HE
11 12

Figure 7 EXPANDED BED FREEBOARD VS EXPANDED BED DEPTH
-------
ro
ro
w

g
•I I
PM

iu
'!'

,
I i
f

: i
V
2.3 + 0.00087 * PDS
0 2 U 6 10 12 lU 16 18 20 22 2U 26 30

Pounds of Dry Solids/HE x 10"3 = PDS
Figure 8 NUMBER OF DEY SLUDGE FEED POINTS VS POUNDS OF DRY SOLIDS PER HOUR
-------
System Electrical Power

The installed and operating horsepower for each reactor in the system

are plotted in Figure 9. Least squares equations fitting the data almost

perfectly are

HPIZI = 320.0 + 2.kk (ZI/1000) + 1.067 ((ZI/1000)2) (23)

0HPZI = 321.55 + 3.39 (ZI/1000) + 0.523 ((ZI/1000)2) (2k)

The total system installed and operating horsepower are given by

HPI = HPIZI(ZII) (25)

0HP = 0HPZI(ZII) (26)

Electrical power costs are given by

CP = 0HP (EPC) (0.7^6) (PCTY) (8760) (27)

where O.jk6 is the conversion factor for converting horsepower to kilowatts

and 8760 is the number of hours in 3&5 days or one year.

Lime Loss Rates

Lime can be lost from the recalcining process by incomplete recovery in

the centrifuge, blowdown of the recalciner CaO bed because of impurities or

stack losses. The sum of these losses is

SLIM = CAP ((PERW + DEWAL)/1(X>] +WJ (28)

The reactor bed blowdown losses (PERW) of Ca0 are required when inert

impurities build up in the system and affect fluidization of the Ca0 bed in

the reactor and system performance. No data was available on blowdown losses,

however, these losses should be very small if essentially pure CaC0 (99$>+ is

fed).
23
-------
10
I
O istalled HP = HPIZI
O Operating HP = OHPZI
HPIZI= 319.99 + 2.U39 (
200
iioo 600 800

Horsepower per Reactor
1000
1200
ZI
1000
Figure 9 DESIGN CAPACITY VS HORRRPOWRR
-------
Dewatering losses (DEWAL) of Ca0 run in the range of 20$ (9). This is

a function of the dewatering device used.

Stack losses (W) of Ca0 are very low in a recalcining system "because of

the multiple cyclone arrangement and high efficiency scrubber used. Stack

losses at the one installation with data were 25 pounds of Ca0 per day or

0.0001786 pounds Ca0 lost per pound Ca0 recovered. Based on this it is

reasonable to assume that the stack losses on a recalciner are negligible.

For example, translating the above loss to yearly cost for lime at $20/ton

gives $91-25/year. Slaking losses do occur, but such data was not available.

Ash

The recalcination process will produce some inert ash material which

must be disposed of. This will include Ca (PO. ) and other non-volatile materials.

For a reactor feed rate of PDS (pounds of dry solids/hr) the reduction in solids

through the process will be caused by C0_ generated from the reaction

(CaC0~ «- Ca0 + C0 ) and by Ca0 recovery from the other solids by slaking.

The C0 generation rate from CaC0_ is

C02 = 2000 (CAP) (UU/56) (29)

where the fraction (M4/56) accounts for the fact that there are hh pounds of

C02 per 56 pounds of Ca0.

Ash formed from the fuel oil or natural gas used to supply heat to the

reactor is negligible. Therefore the total ash which must be handled and

disposed of is

PAPH = PDS - CAP(2000) - C02 + (w + PERW/100)(2000)(CAP)

- PDS(PVS)/100 (30)
-------
where CAP (2000) is the Ca0 recovery rate and C0 is the gas generation rate

from the CaCJzL reaction to Ca0 + C0_. The fourth term in Equation (30) is

the rate of Ca0 loss from the system which must be treated as ash and the

fifth term is the rate of combustion of the volatile solids fed to the

reactor in the dry solids.

Reactor Heat Balance

The heat transferred to the fluidizing air from the pelletized lime in

the cooler section is

QAPR = CAP(2000)(.21?)(1650 - ^00) (31)

This equation states that the Ca0 discharged through the reactor has a

specific heat of 0.21? Bbu/pound °P and is cooled from l650°F to ^00°F by

the fludizing air. The fluidizing air is heated to approximately ^00°F

in the cooler.

Each reactor requires heat from a fuel (usually number 6 fuel oil) to

recalcine the lime. The heat from a fuel required by each reactor in the

system is

QF0 = I SUMQ - QSL(PDS) - QAPR j /ZII (32)
L. J

Thus the fuel must supply the gross heat required by each reactor in the

calcining zone less the heat rate supplied by the volatiles in the feed to

the reactor less the heat recovered by the fluidizing air in the cooler.

System Costs

Electrical

Electrical power costs are given by Equation (27).
26
-------
Fuel

Fuel costs for each reactor in the system is given "by

CF0 = WF0(PCTY)(8760)(FC/10 ) (33)

and fuel costs for the system of ZII reactors is

CF0I = CF0 (ZII) (3*0

Operating and Maintenance

The yearly cost of operating labor per year is

CL = 0.25(CLR)(PCTY)(ZII)(8760) (35)

for the system. This is based on observations of the operating procedure

used for both fluidized bed incinerators and recalciners. The average

operator must be available at all times in case of emergencies. However,

the operation of a fluidized bed system is almost completely automated. Thus

an operator need only spend about one hour in every four operating hours

checking instrumentation and making minor adjustments. The remainder of the

time the operator is available for other duty. Equation (35) was developed

with the assumption that one operator per reactor is needed for 25$ of the

operating time. It is entirely possible that one operator could handle four

reactors in a system unless an emergency arose in which case another man

would be required. The optimum labor force for this type of equipment

should be one operator for every two to four reactors. The operator should

be used for routine preventive maintenance in his spare time. At least

one maintenance personnel should be used for each h to 8 reactors. Eequired

yearly maintenance labor costs for the system (ZII reactors) are estimated as

CLM = CIMR(PCTY)(876o)(ZIl)/8 (36)
27
-------
Note that Equations (35) and (3&) account for only the labor required to

keep the reactors running properly. No attempt is made to estimate how

efficiently personnel are used. For example, if an operator is required for

two hours per day it is assumed that he is doing other useful work during

the remaining six hours and not charging idle time to the operating cost.

If this is not true for a particular installation then these equations must

be modified to reflect the true labor situation.

Maintenance on specialized equipment such as instrumentation will usually

be done by a service organization rather than plant personnel. It is estimated

that one man hour of service labor is required for every 150 hours of reactor

operation. Therefore the yearly system cost of maintenance service labor is

estimated as

CLMA = CIMS(PCTY)(8760)(ZIl)/8 (37)

The cost of operating a recalcining system for one year is

C0 = CL + CP + CF0I (38)

Yearly maintenance costs for the recalcining system are

CM = CIM + CIMA + CER (39)

where CER is the cost of equipment which must be replaced such as thermo-

couples and other minor parts. The cost of equipment replacement was low

although costs were not available. Therefore CER was assumed as $1 per

day or CER = 365 (ZIl).

Makeup Lime and Solids Disposal

Without a recalcining system the yearly cost of new lime and the cost

of solids disposal (CaC0._ plus other solids included in PDS) is
28
-------
CLIME = (CCA0(CAP) + DC (PDS/2000))(PCTY)(8760)

When a recalciner is used, the yearly cost of lime makeup to the system

and ash disposal can be expressed as

CIMUV = (CSLIM + ASHDC)(PCTY) (8760) (Hi)

where

CSLIM = SLIM (CCA0)

and

ASHDC = DC (PAPH)/2000

Equipment Capital Costs

Figure 10 shows the cost relation developed from the available field

data as

EC = 0.0219 (SUMQN) + 37100.0 (MO

where EC is the cost adjusted to February, 1968 dollars. The cost adjustments

were made using the local Sewage Treatment Plant Cost Index of the Department

of the Interior and bringing the costs to local values for February, 1968.

Then the local values were adjusted to the national average values using the

respective Sewage Treatment Plant Cost Index.

Installation and Consulting Fees

Based on available information, an installation fee of 10$ must be

added to the equipment cost . Also a consulting engineers fee of 10% of

the sum of the system equipment cost plus installation fee must also be
added . Therefore
CI = EC/10

CEF - (EC + CI)/10
1. Data from a conversation with Mr. Stewart Peterson, N.E. Region Program
Director, FWPCA, Boston, Mass.
29
-------
(..)
o

I
o
• I
:
.*
-8
! '
n
' i
i •
d
;i,
. I
•I I
>' >
1000

900

800

700

600

500

Uoo

300

200

100

'
EC = 0.0219 (SUMQN) + 37100.0
Normal Price (quoted)
- Discount Price
1 I
6 8 10 12 ih 16 18 20 22 2k 26 28 30 32
System Net Input, Btu/hr x 10~6 == SUMQN
Figure 10 CAPITAL EQUIPMENT COST YS SYSTEM NET INPUT TO BED
Equipment Cost adjusted from purchase date and location of installation
to Feb., 1968 and national average Sewage Treatment Plant Cost Index of
the Department of the Interior. This Index is presented quarterly in the
Engineering News-Record.
-------
and the total system capital cost is

TSC = EC + CEF (U?)

in February, 1968 dollars. This cost can be adjusted to any year by using

the national average Sewage Treatment Plant Construction Cost Index of

the Department of the Interior. This index appears quarterly in the

Engineering News Record Magazine.

Total Cost of Maintenance and Operation

The total yearly system maintenance and operating cost is

TCM0 = CM + C0 (kQ)

The total yearly cost of maintenance, operation, lime makeup and solid

waste (ash) disposal with a recalciner, from the inlet of the dewatering

device through the exhaust stack is

TCLIW = TCM0 + CIMUW
31
-------
COMPUTER PROGRAM

Li st ing erf Program

The complete program developed for use as a subroutine is listed below

in Fortran IV.

Flow Chart

The flow chart for the computer program developed is shown in Figure 11.
32
-------
// FOR
*IDCS(CARD»1132PRINTER*
*LIST ALL
REAL NFP
C LI^E RECALCINATIOM IM FLUIDIZED BED REACTOR
10 FO*MAT(1HO»'COSTS DO .NOT INCLUDE BUILDINGS OR LAND REQUIKtD FOR
1UIPYENT1)
111 FORMAT!1HO,'COSTS DO NOT INCLUDE LAND FOR STORAGE OF WASTES')
11 FORMAT(2FJ0.4)
12 FORMAT (1H<'.« SYSTEM IS TOO SMALL TO BE ACCURATELY SIZED BY THIS

13
14
15
100
110

120

130

140

150
FORMAT UH*»' CASE'»I3)
FORMAT(5Fi0.4>
FORMAT (1 HO • 8 ( 5F 16. 4 , / / , IX ) )
FORMAT) lHOt6Fl6. 4}
1=0
REAQ!2»14 ) X » Y » PCT Y . FC *EPC
READ(2»14 ) CLR»CLMR,CLMS»DC»PERW
READ(?.»14 ) CAP»QSL»YRS»CCAO»W
READ (2 .11 JDEWALtPvS
1 = 1+1
,VRITE(3»13 )I
ZII-1.
PI=3. 14159
POS=CAP*2000./( X*Y)
IF(ODS-4000. > 110. 120*120
WRITE(3»12 )
GO TO 180
SUMQN=QCAO*CAP
EMDQ= (?.69*io»**6)*CAp
SUMOI=SUWQN/ZII
AGC=SUMQ 1/24 1000.
DGC=(4.*AGC/PI )**.5
IF(DGC-16.) 150 » 153 » 140
ZI I=ZII+1.
GO TO 130
ZI=»DS/ZII
DFC=DGC
DFO= (DGC-1.5 J/.49
AFO= 'PI*OFO**2) /4.
VE=SUMQI/23700.
VS=VE/l-5
HE=10.
HS=HE/1.5
HFXP=.5
HP = 3.
HC=8.5
HF=16.
FLOAT< I F IX ( 2. 3 + 0. 000 R7*Z I +0.5 00 001 ) )
le(NFP) 160*160.170
LIME
L I ME
EULIME
LIME
LIME
LIME
PRLIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LI ME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
LIME
. LIME
L I ME
L I ME
LIME
L I ME
L I ME
LIME
LIME
LIME
LIME
LI^-E
L I ME
LIME
LIME
LIME
LIME
1
2
3
4
5
6
7
a
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
2B
29
30
31
32
33
34
35
36
37
3d
39
40
41
42
43
44
45
46
47
48
49
50
33
-------
160 NFP»1. LIME 51
170 HPIZI=320.+2.439*CZI/1000.)+1.0665*(ZI/1000.)**2 LIME 52
OHPZI=321.6+3.39*(ZI/1000.)+0.523*(ZI/1000«)**2 LIME 53
HPI=HPIZI*ZII LIME 54
OHP«OHPZI*ZII LIME 55
CP=OHP*EPC*0.746*PCTY*8760. LIME 56
SLIM*CAP*«(PERW+DEWAL)/100, >+W) LIME 57
C02«2000.*CAP*44./56. LIME 58
PAPH=PDS-CAP*2000.-C02-MW+PERW/100.)*2000.*CAP-PDS*PVS/100. LIME 59
QAPR=CAP*2000.*.217*11650.-400.) LIME 60
QFO»(SUMQ-QSL*PDS-QAPR)/ZII LIME 61
CFO«QFO*PCTY*8760.*FC/10.**6 LIME 62
CFOI«CFO*ZII LIME 63
CL=.25*CLR*PCTY*ZII*8760. LIME 64
CLM*CLMR*PCTY*8760.*ZII/8t LIME 65
CLMA*CLMS*PCTY*8760.*ZII/150. LIME 66
CO=CL+CP+CFOI LIME 67
CER«3o5.*ZII LIME 68
CM=CLM+CLMA+CER LIME 69
CLIMF=(CCAO*CAP+DC*PDS/2000«)*PCTY*8760. LIME 70
ASHDC=DC*PAPH/2000, LIME 71
CSLIM=SLIM*CCAO LIME 72
CLMUW=(CSLIM+ASHDC)*PCTY*8760. LIME 73
EC»0.0219*SUMQN+37100. LIME 74
CI=EC/10. LIME 75
CFF=(EC+CI)/10« LIME 76
TSC-EC+CI^CEF LIME 77
TCMO«OH-CO LIME 78
TCLIW=TCMO+CLMUW LIME 79
WRITEOtlU ) LIME 80
WRITE(3.111)
WRITE(3tl5 ) X»Y.PCTY»FC.EPC»CLR»CLMR»CLMS»DC»PERW»CAP»QSL»YRS»CCLIME 81
1AO»PDS»ZIItSUMON»SUMQ»DGC*ZI»DFO»VE»ORH»NFP»HPIZI»OHPZI»C02»PAPH»ULIME 82
2APR.QFOtCFO.CFOI»CP»CL»CLM,CLMA.CO.CER.EC»TSC.CM LIME 83
WRITEJ3.16 ) CLIME.CLMUW.TCLIW.W.DEWAL.PVS LIME 84
ISO PAUSE 1111 LIME 85
CALL DATSWU.MORE) LIME 86
GO TO ( 100. 190),MORE LIME 87
190 C*LL EXIT LIME 88
END LIME 89
-------
Read X, Y, PCTY, FC,
EPC, CLR, CLMR, CLMS,
DC, PERW, CAP, QSL,
YRS, CCA0, W, DEWAL,
PVS
ZI, DFC, DF0,
AF0, VE, VS, HE
HS, HEXP, HP, HC,
HF, 0RH, NFP
HPIZI, 0HPI, HPI, 0HP, CP,
SLIM, C$2, PAPH, QAPB, QF0,
CF0, CF0I, CL, CLM, CLMA,
C0, CER, CM, CLIME, ASHDC,
CSLIM, CLMUW, EC, CI, CEF,
TSC, TCM0, TCUW
I =
I +
1
N. WRITE CASE I f
ZII, PI, PDS
ffiIIE TOO
SMALL
1
flRITE
COSTS DO NOT INCLUDE
BUILDINGS OK LAND FOR
'EQUIPMENT
COSTS DO NOT INCLUDE
LAND FOB WASTE
Figure 11 FLOW CHART

35
-------
How to Use Program

Operation

The operation of the computer program requires an input of four data

cards. Samples of these data cards are shown in Figure 12. Also data

switch k must be set OFF for normal machine exit and ON for additional data

input (i.e. cases 1,2,3, etc.). Nothing else is required of the operator.

The input stream to be used is the material leaving the dewatering device but

with zero water content (since water is completely removed in the cage mill).

The output data generated by the input data in Figure 12 is shown in

Figure 13.

Reactor Sizing Limit

As with any mechanical equipment there is a maximum tolerable size above

which a fluidized bed reactor cannot be economically constructed using standard

available materials. The physical size and operating stress combine to make

this limit apparently a unit with a reactor calciner grid diameter of l6 feet.

This is based on observations of fluidized bed equipment installed at the

23 locations from which data were obtained in performances of FWPCA contract

14-12-^15. If a larger than 16 feet diameter reactor is required a series

of reactors having equal diameters is selected by iteration in the program.

The number of equal diameter reactors selected per system is ZII. The

capacity of each reactor in pounds of dry solids per hour is then

ZI = PDS/ZII

The system cost curves are based on field data on equipment with feed capa-

cities from approximately ^000 to 25,000 pounds of dry solids per hour (Figure 8)
36
-------
CARD #1 X, Y> PCTY, FC, EPC
CARD #2 CLR, CLMR, CIMS, DC, PERW
CARD #3 CAP, QSL, YRS, CCA0, W
CARD #k DEWAL, PVS
.156 .75 .25 i.20
2. 8.50 4. 5.
1
.1 500. 20. 29.
,01 10.

.06
10.
V*
.01

CARD #

CASE 1

CASE 1 " 3

CASE 1 " **•
0 0 11 0 00 00 0 0 0 0 0 00 00 0 0 0 D 0 00000 0 0 009000 000 0 0 0000tOO 0 0 0 03 BOO 0 00 0 000000 0 0 0 09000 0 0 0 00
1 2 ' 4 S 5 ' ' ' 10 » "i>iiii]inin11i111in11 11 11 i n 11 111 i i i 111 i 11 11 i n i 11 i 1111 j i i 11 i i i

2222222222222222222 2 2222222222222222222? 222222222222222222222222222222222222 2222

33333333333333 3333333333333333333333333333333333333333333333333333333333333333
CASE 1

.S6
-
i
1.

.01
.75
2.50

500.
10,
.25
4.

20.

1.26
5".

20.

.06
10.
^
.01

CARD #

j CASE 2 -j^

CASE 2. 2

CASE 2 3

CASE 2 ' 1+
0 0 0 9 0 0 ' 0 0 0 0 0 0 0 ' 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D 0 G 0 H 0 0 0 0 0 D 0 0 0 0 0 0 0 0 0 0 0 0 0
1 2 3 4 5 S / « 9 10 II 12 13 14 15 15 1) II 13 !0 II !! 23 !4 25 26 27 21 29 30 31 32 33 34 35 36 37 a 39 40 II 42 43 44 45 »6 47 49 40 50 51 52 53 54 55 5F 57 58 59 SO SI (2 83 64 55 SS 6) 68 69 JO II 11 73 7< 75 76 7! 78 79 TO

1 11 1 1 1 1 " 1 1 1 1 i * 1 1 1 11 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 I I 1 1 1 1 1 1 1 1 1 1 1 1 H I 1 1 1 1 1 1 1 I 1 I 1 1 1 1 I II 11 1 1 1 1 1 1

22222222222222222222222222222222222222222222222222222222222222222222222222222222

3 3 3 3 3 ' 3 3 3 3 3 3 3 3 3 ' 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 I 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
CASE 2.
Figure 12 SAMPLE INPUT DATA CARDS
37
-------
CASE 1

SYSTEM IS TOO SMALL TO BE ACCURATELY SIZED BY THIS PROGRAM
CASE 2

COSTS DO NOT INCLUDE BUILDINGS OK LAND REQUIRED FOR EQUIPMENT

COSTS DO NOT INCLUDE LAND FOR STORAGE OF WASTES
u>
oo
0.5600

2.0000

1.0000

7.4278

349.6022

12526.4804

58.4000

1107.7751

69871. 437*'
0.7500

2.5000

500.0000

5000001.0136

210.9704

1571.4287

12526*4804

47891.0157

9937.5898
0.2500

4.0000

20.0000

7690000.0117

38.5000

934.2852

34269.5391

365.0000

58936.3750
1.2000

5.0000

20.0000

5.1396

6.0000

542500.0014

1095.0002

146600.0004

0.0100
0.0600

10.0000

4761.9052

355.7979

4766547.0136

684.3751

177385.9691

0.0100
10.0000
Figure 13 OUTPUT DATA GENERATED FROM INPUT DATA SHOWN ON FIGURE 12
-------
Accuracy of the relationships developed is uncertain beyond these limits. It

is estimated that reasonable approximations can be attained at higher capacities

since the reactors are limited to 16 feet calciner grid diameter and systems

are built in multiples of similar reactors.

Figure Ik shows a plot of the capital cost of the recalcination system

in Feb. 68 dollars versus system capacity.
39
-------
150
!
I':
m

;
'

:
•i i

i
-
(
i.,
'. "
•
' <
System Cost vs Capacity

Lbs CaC0
"Assumed Y - 0.75
Lb dry solids
Note: The range of field

data obtained is from

to 25,000 pounds of dry

solids per hour assuming

Y = 0.75.
6 10 12 lU 16 18 20 22 2U 26 30

Cost in Millions of Dollars

Figure lU SYSTEM COST IE MILLIONS OF DOLLARS VS CAPACITY
-------
CONCLUSIONS AND RECOMMENDATIONS

Performance of the System

In general, personnel at the installations surveyed were pleased with

the performance of the fluidized bed recalcination system. The users of

this equipment are mainly concerned with operating cost ($/ton Ca0) as

compared to the cost of makeup lime delivered to the storage bins. There

are indications that with the current design practice fluidized "bed recal-

ciners can be operated at about k-0% over design ratings.

No fluidized bed recalciners are presently being used for lime recovery

at sewage treatment plants. It may be possible to recover lime by recalcina-

tion in the same reactor used to incinerate the primary sludge. If so a

dual purpose incineration-recalcination process would greatly reduce the

recalcination costs. Experience at Blue Plains with a multiple hearth

recalciner indicates that only recalcination of relatively pure CaC0,j can

be achieved. Quite possibly this will be true for the fluidized bed process.

Then lime recovery from CaC0^ will be limited to the tertiary process. The

computer program developed will adequately size and cost the fluidized bed

system required for primary or tertiary lime recalcination provided a Ca0

pelletized bed is used in the reactor and the equipment is similar to that

upon which the model is based.

Since there were no fluidized bed recalciners in operation at sewage

plants information on lime loss rates from such a system were not available.

Based on the survey information the lime loss rate in the dewatering process
-------
is (DEWAL). 20$. The lime loss rate caused by required bed blowdown (PERW)

to remove lumps of impurities from the bed is roughly estimated to be in

the range of less than 1% for relatively pure CaC0.-, feed. It should be higher

for impure CaCjZL feed. Stack losses (w) are negligible because gas cyclone

and scrubber efficiencies are very high (99+%).

Slaking difficulties were encountered at some plants because of slaking

"being attempted at too low a temperature.

Factors to be Considered

For a fluidized bed recalciner, the cost of operating and maintenance labor

varies depending on the situation. In some cases permanent operators and

maintenance personnel are assigned on the basis of peak work loads rather

than normal work loads. In general, two man-hours per day should be sufficient

to operate each recalciner. When problems occur, men must be available to

correct them. Thus if a man is used to operate a system only part-time, he

and other personnel must be available on short notice to tend to any mal-

function and maintenance problems of the reactor system.

The recalcination system with the cost of land for the system and related

disposal areas, buildings to house equipment, lime makeup, operation and main-

tenance must "be weighed against a non-recalcining installation with greater

lime makeup costs, larger storage areas for makeup lime and CaC0_, and greater

solids disposal costs.

The efficiency of combustion equipment will vary depending on how it is

operated. The computer program developed assumes that near-optimum performance.
-------
will be maintained. Excess air, bed conditions, pelletizing efficiency

(i.e., soda ash concentration in bed), and use of waste heat in cooler or

pub mill will play important parts in the operating efficiency. Optimum

efficiency is seven to eight million Btu's per ton of recalcined Ca0.

In the installations surveyed, the capital costs of buildings, equipment,

land and taxes were apparently neglected (or unimportant because of tax

depreciation or other reasons). In general, the volume of the building

required to house a fluidized bed recalcination system is roughly four times

the volume of the reactor alone. A clearance of about ten feet is allowed

both above and below the reactor.

Equipment Design

The system analyzed in this program includes a pellet cooler below the

calcining zone. All fluidized bed recalcination systems should have such a

cooler because:

l) the heat removal from the pellets is required so they can be

handled and stored for reuse,

2) the heat removed from the pellets would otherwise be wasted

if it were not used to preheat the fluidizing air and reduce

fuel costs.

Care should be taken in design of the slaking process to insure that

sufficiently high slaking temperatures are provided. This can be accomplished

by using the heat from the hot exhaust gases leaving the reactor at about

1600°F. These gases are quenched with air or water to 1000°F before entering

the cage mill. It would be wise to use the wasted heat for slaking or some

other function such as fluidizing air preheat after the cooler section.
-------
BIBLIOGRAPHY

1. Graham, R. E., "Lime Recalcining at Alvarado Lick Sludge Disposal Problem",
Water Works Engineering, July, 19^2, p. 571.

2. Crow, W. B., "Techniques and Economics of Calcining Softening Sludges",
Journal of AWWA, March, 1960, p. 322.

3. Mahlie, W. S., "Use and Handling of Lime in Water and Waste Treatment",
Public Works, Nov., 19^3, p. 96.

k. Bauer, W. G., "Fluidization - Multipurpose Process Tool", Pit and Quarry,
June, 1965, p. 6ij-.

5. Lee, B. S. et. al., "Kinetics of Particle Growth in a Fluidized Calciner",
A.I.Ch.E. Journal, Vol. 8, No. 1, March, 1962, p. 53-

6. Grimmet, E. S., "Kinetics of Particle Growth in the Fluidized Bed Calcin-
ation Process", A.E.Ch.E. Journal, Vol. 10, No. 5, Sept., 19^, p. 717-

7. Trauffer, W. E., "Florida's New 200 TPD Lime Plant", Pit and Quarry, May,
1962, p. 126.

8. Brandt, W. M. et. al., "The Fluidized Solids Lime Process", Tappi,
Vol. 1+7, No. 5, May 196U, p. 137A.

9. Herod, B. C., "Lime Reclaiming Plant Utilizes Fluidizing Techniques",
Pit and Quarry, Oct., 1958, p. 120.

10. "Chemical Lime's Fluidized Solids Calcining Plant One Year Later", Pit and
Quarry, May, 1963, p. 122.

11. Haltz, H. J. et. al., "First Fluidized Solids Lime Mud Recovery System in
a Paper Mill", Pit and Quarry, May, 196U, p. 116.

12. King, D. L., "Calcining Phosphate Rock", Chemical Engineering Progress,
Vol. 55, No. 12, Dec., 1959, P- 77.

13. Cooper, E. D. et. al., "Pilot — and Plant Scale Fluidized Bed Calciners",
Chemical Engineering Progress, Vol. 6l, No. 7, July, 19^5, p. 89.

1^. Stuart, H. H. and Bailey, R. E., "Performance Study of a Lime Kiln and
Scrubber Installation", Tappi, Vol. U8, No. 5, May 1965, p. 1014-A.

15. Hannan, P. J.. "A Flash Drying System for Lime Mud", Tappi, Vol. ^7, No. 2,
February, 1964, p. 162A.

16. Hotz, H. J. et. al., "Fluidized Solids Lime Mud Recovery at S. D. Warren Co.",
Tappir, Vol. Vf, No. 11, Nov., 196U, p.
17. Moran, J. S. and Wall, C. J., "Operating Parameters of Fluidized Bed
Lime Mud Returning System", Tappi, Vol. ^9, No. 3, p. 89A,
-------
18. Lindsay, G. C., "New Florida Plant Boils Lime", Rock Products. April.
1962, p. 83.

19. Ironman, R., "Fluidization - Dominant Trend in Today's European Lime
Industry", Rock Products Mining and Processing, March, 196*1, p. 95.

20. Preistly, R. J., "How Good is the Fluosolids Reactor", Rock Products,
July, 1965, p. 72.

21. "Use of Fluosolids Kilns Increasing" C and FN, Oct., 21, 1963, p. 56.

22. "I&EC Reports and Comments, New Application for Fluidized Calciners",
Industrial and Engineering Chemistry, Vol. 56, No. 9, Sept., 196k, p. 9.

23. "Uses Expanded for Fluosolids System", C & EN, July 26, 1965, p. k3.

2k. Havighorst, C. R., "Improved Fluid Bed Calcination Hikes Lime Production",
Chemical Engineering, October 26, 196*4-, p. 10*4-.

25. "Fluidized-Bed Furnaces", Chemical Engineering, April 11, 1966, p. 171.

26. Herod, B. C., "Lime Industry Pacesetter Takes Another Impressive Step
Forward", Pit and Quarry, November, 1963, p. 87.

27. Herod, B. C., "Oxford Paper Company Now Reclaims up to 90 percent of
Progress Lime with 150 TPD. Calciner at Rumford, Maine", Pit and Quarry,
August, 1963, P. 105.

28. "Onoda Cement Company's Lime Calcination Process in Cement Manufacture",
Pit and Quarry, July, 1965, p. 185.

29. Herod, B. C., "Lime Produced, Recovered in City of Dayton's New Calcinating
Plant", Pit and Quarry, May 1956, p. 128.

30. Boynton, R. S., "European Lime Manufacture", Pit and Quarry, May, I960, p. 12*4-.

31. Levine, S., "Unique Calciner Breaks all the Rules", Rock Products, Dec. 1963,
p. 50.

32. "Reclaiming Lime in Caustic Production", Automation, Nov., 1962, p. 76.

33. Huttl, J. B., "Kennecott Adds Unique Lime Plant to Hayden Reduction Works",
E & MJ, Vol. 163, No. 11, p. 9**.

3*4-. Beeken, D. ¥., "Fluidized Bed Techniques: Inception, Growth and Future
Prospects", The Industrial Chemist, June, 1958, p. 329-

35. Scott, J. C., "Ann Arbor's Recalcining Process and Problems", AWWA Journal,
June, 1969, p. 285.

36. Albertson, 0. E., "Disposal of Waste Material by Combustion in an Inert
Fluidized Bed", Filed March 31, 196*4-, Released May 16, 1967, U. S. Patent
No. 3,319,587.

*t-5
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TERMINOLOGY
AFC

AGC

AF0

ASHDC

CAP

CCA0

CEF

CER

CF0

CF0I

CLIME

CLIMR

CLM

CLMA
Cross-sectional area of grid in calciner of each reactor,
ft2

Cross-sectional area of freeboard in calciner of each
reactor, ft2

Cross-sectional area of freeboard zone above calcining section
in each reactor, ft2

Total system ash disposal cost, current $/hr

System calcining design capacity (all reactors combined),
tons CaO/hr

Cost/ton lime delivered to location, current $/ton

Consulting engineers fee for total recalcining system,
Feb. 1968 $

Yearly cost of maintenance for total recalcining system,
current $/yr

Cost of fuel for operation of each reactor over a one-year
period, current $

Cost of fuel for operation of all reactors (ZIl) in system
handling PDS over one-year period, current $

Installation cost for total system less building, Feb. 1968 $

Cost of operating labor per year for total recalcining system,
each reactor requires separate operator for 1 hr in each h hrs
of operation, $/yr

Total yearly purchased and disposal cost of new lime and other
process solids, current $/yr without recalciner

Total yearly purchased lime and disposal cost of recalcination
waste products for plant with recalciner, current $/yr

Yearly cost of maintenance labor for total system, each reactor
requires 1 hr in 8 hrs of operation, current $/yr

Yearly cost of maintenance service labor for total system,
current $/yr
CLMR
Cost of maintenance labor rate, current $/man hr
-------
cms

CIMUW

C02

CLR

CSLIM

DEWAL

DFC

DF0

END0

EPC

HEXP
Cost of maintenance service labor rate, current $/man hr

Cost of lime makeup and solids disposal with recalciner,
current $/yr

Yearly cost of maintenance for total recalcining system,
current $/yr

Yearly cost of operation of total system, current $/yr

Carbon dioxide liberated in reaction of CaC0 Ca0 +
C0p for total system capacity, pounds/hr

Yearly cost of electrical power for total recalcining
system, current $/yr

Cost of operating labor, current $/man hr

Cost of lime lost from system be dewatering, blowdown of
bed and stack losses, current $/hr

Disposal cost of solid wastes for removal from plant site,
current $/ton

Percent of lime lost in dewatering process, 100 (#Ca0 lost)
per $ CaO recovered

Freeboard diameter in calciner of each reactor, ft

Diameter of Freeboard zone above calcining section in each
reactor, ft

Total system capital equipment cost for equipment from and
including dewatering device to stack inlet not including land
and buildings required, Feb. 1968 $

Endothermic heat of reaction (CaC0 Ca0 + C0 ), (total for
all reactors in system), Btu/hr

Electrical power cost, current $/KW hr

Fuel cost per million Btu1 s, current $

Height of cooler section in each reactor, ft

Depth of expanded fluidized bed in each reactor, ft

Height of expansion section between calcining and freeboard
zone in each reactor, ft
HF
Height of freeboard above calcining section in each reactor, ft
-------
HP

HPT

HPIZI

NFP

0HP

0HPZI

0KH

PAPH

PCTY
PCS

PERW

PVS

QAPR

QCA0

QF0

QSL

SLIM

SUMQ
Height of air distribution plenum in each reactor, ft

Installed HP in total system HP

Installed HP per reactor, HP

Static depth of fluidized bed in each reactor, ft

Number of points at which Ca0 sludge is fed into the
fluidized bed in each reactor, dimensionless

Operating HP in total system, HP

Operating HP per reactor, HP

Overall height of each reactor, ft

Pounds ash per hour, as calcium phosphate and other wastes
from total system, pounds/hr

Fraction of year, week of month to be operated, hrs
operated/hrs in year (total hours, not work hours);
i.e., continuous operation for one year is for
8760 hrs/yr. For 1/2 time, PCTY = .5 and operating
time = ^380 hrs/yr.

Total design pounds of dry solids per hour fed to all
reactors in system, pounds/hr

Percent of lime lost in blowdown for periodic removal of
inerts in all recalciners, 100(#Ca0 lost)/#Ca0 recovered.

Percent volatile solids in sludge, 100(pound VS)/pounds
dry solids

Total heat supplied to calcining process through air
preheating in the cooler/coolers section(s) of all
reactors combined, Btu/hr

Gross heat minus endothermic heat of Ca0 required per ton
of CaO produced, Btu/ton Ca0

Heat required from fuel in each reactor of system, Btu/hr

Sludge heat input (lower heating value), Btu/pound of dry
solids

Lime lost from system by dewatering, blowdown of bed and stack
losses, tons/hr

Gross heat input to fluidized bed for all reactors combined
in system considered, Btu/hr
-------
SUMQI = Design net heat input to each recalciner in system,
Btu/hr

SUMQN = Net heat input to adiabatic fluidized "bed (total for all
reactors in system), gross heat minus endothermic heat of
reaction, Btu/hr

TCLIW = Total yearly cost of operation, maintenance, lime makeup
and solids disposal with recalciner, from inlet to centrifuge
or vacuum filter, current $/yr

TCM0 = Total yearly system operating and maintenance cost, current $/yr

TSC = Total system cost including installation and consultants fees
less "building and land, Feb. 1968 $
3
VE = Expanded volume of fluidized bed in each reactor, ft
•3
VS = Static volume of each fluidized bed, ft

¥ = Pounds of Ca0 lost through stack per pound Ca0 recovered

X - Pounds Ca0 per pound CaC0.~ in feed to reactors =0.^6

Y = Pounds CaC0_ per pound dry solids in feed to reactors

YES = Estimated operating life of recalciner, yrs

ZI = Design pounds of dry solids per hour each recalciner in the
system handles, pounds/hr

ZII = Number of recalciners in system required to handle the design
sludge capacity
ft U. S. GOVERNMENT PRINTING OFFICE ; 1970 O - 408-942
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