The Rocketdyne Division of Rockwell International Corporation is conducting a program for the engineering, fabrication, and testing of an experimental/prototype high-capacity, high-pressure centrifugal slurry feed pump for coal liquefaction purposes. The abrasion problems in a centrifugal slurry pump are primarily due to the manner in which the hard, solid particles contained in the slurry are transported through the hydraulic flow passages within the pump. The abrasive particles can create scraping, grinding, cutting, and sandblasting effects on the various exposed parts of the pump. These critical areas involving abrasion and impact erosion wear problems in a centrifugal pump are being addressed by Rocketdyne. The mechanisms of abrasion and erosion are being studied through hydrodynamic analysis, materials evaluation, and advanced design concepts

Davis, D. E.

Gilman, H. H.

Wong, G. S.

English

NASA Technical Reports Server

COAL/OIL SLURRY F E E D  PUMP 
D. E.  Davis  
G. S. Wong 
Rockwell  1nte r n a t i o n a l / ~ o c k e  td-8 ne 
Divis ion 
Canoga Park,  California 
H. H. Gilman 
E l e c t r i c  Power  R e s e a r c h  Institute 
P a l o  Alto,  California 
https://ntrs.nasa.gov/search.jsp?R=19780005323 2020-03-20T12:36:58+00:00Z
ROCKETDYNE ' S  ADVANCED COAL SLURRY PUMP 1 NG PROGRAM 
by 
D r .  D. E. Davis*, U. 5 .  Wong,** and H. H. Gilman*** 
ABSTRACT 
The Rocketdyne D iv is ion  o f  Rockwell ln te rna t  ional Corporation i s  conducting 
a program for  the engineering, fabr ica t ion ,  and tes t i ng  of  an experimental/ 
prototype high-cepaci ty  , high-pressure cent r i fuga l  s l u r r y  feed pump fo r  coal 
l iquefact ion purposes. The program i s  being conducted f o r  the E l e c t r i c  Power 
Research l n s t i t u t e  (EPRI) o f  Palo A l to ,  Ca l i fo rn ia .  
The abrasion problems i n  a cent r i fuga l  s l u r r y  pump are p r imar i l y  due t o  the 
manner i n  which the hard, s o l i d  p a r t i c l e s  contained i n  the s l u r r y  are trans- 
ported through the hydrau!ic f low passages w i t h i n  the pump. The abrasive 
p a r t i c l e s  can create scraping, gr inding, cu t t ing ,  and sandblasting e f fec ts  on 
the various exposed par ts  of  the pump. These c r i t i c a l  areas involv ing abra- 
sion and impact erosion wear problems I n  a cent r i fuga l  pump are being addressed 
by Rocketdyne. The mechanisms o f  abrasion and erosion are being studied 
through hydrodynamic analysis,  mater ia ls  evaluation, and advanced d e q i y  
concepts . 
1 NTRODUCT 1 ON 
With the impending shortage and increasing cost of energy resources, the con- 
version of coal t o  a l te rna te  usable forms such as 1 iquefact ion and gas i f  ica- 
t i o n  are increasing i n  importance. Because of t h i s  urgent need, the Fossi 1 
* Program Manager Coal Slurry  Pump Program, Rocketdyne D iv is ion ,  Rockwe 1 1 
ln ternat  ional  Corporation 
** Project  Engineer, Advanced Pump Systems, Rocketdyne 
*** Engineering Manager, Advanced Fossi 1 Power Systems, E l e c t r i c  Pwer  
Research I n s t i t u t e  
Fuel and Advanced Systems Div is ion  of the E l e c t r i c  Power Research I n s t i t u t e  
i s  sponsoring a pro jec t  for  ear ly  development of a s l u r r y  feed pump for  coal 
l iquefact ion. The coal l iquefact ion processes present ly being considered 
f o r  commercial development general ly requi re high-pressure coal s l u r r y  feed 
t o  be supplied t o  a preheater and reactor a t  h igh capaci t ies.  
The operat ing SRC p i l o t  p lan ts  a t  Wi lsonv i l le ,  Alabama, and Tacoma, Washing- 
ton, cur ren t ly  use convent ionai  law-capaci t y  , rec procat ing feed pumps. 
However, the future scaleup of the present type of feed pump t o  comnercial- 
s ize  p lants would mean using an extremely large number o f  rec iprocat ing pmps 
i n  p a r a l l e l  w i t h  the h igh cap i ta l  and maintenance costs associated w i t h  mul- 
t i p l e  un i ts .  Therefore, high-volume cen t r i f uga l  pumps producing h igh  pres- 
sures are considered t o  be excel len t  candidates fo r  addressing the above 
problems w i t h  respect t o  commercial l i que fac t i on  p lan t  feed systems. Although 
cent r i fuga l  pumps are advantageous for high-volume appl icat ions,  current  
designs are subject t o  excessive i n te rna l  wear because o f  h igh  ve loc i t i es .  
The primary approach being taken i n  the current  EPRl prcgram i s  t o  conduct a 
comprehensive engineering study of  the problems o f  pumping h igh ly  abrasive 
coa l /o i l  s l u r r i e s .  A concentrated e f f o r t  i s  made t o  i den t i f y  the problems by 
making maximun use o f  the data, knowledge, technology, and experience tha t  
e x i s t  i n  industry and a t  Rocketdyne. 
The present tes t  program and design study are cont inuing w i t h  the u l t imate  
goal of prov id ing a re1 iab le  cent r i fuga l  coal s l u r r y  feed pump designed f o r  
the f o l  lav ing condit ions: 
a Capacity 
Feed Rate 
Pressure 
a Temperature 
a Coal/Oil S lu r r y  
Concen t r a t  ion 
Speci f ic  Gravi ty  
Viscosi ty  
So l i d  Size 
SO00 gpm 
50 t o  100% 
3000 ps i  
550'~ 
50% (by weight) 
1.20 
25 t o  50 c.p. 
200 mesh 
Operation 
Minor Maintenance 6 months 
Major Overhaul 1 year 
The r e s u i i t  and data obtained i n  the study program on s l u r r y  flow, mater ia l  
erosion, and promising high-wear-resistant mater ia ls  and coatings v i l l  be 
u t l l  i r e d  i n  the prototype s l u r r y  pump study t o  ensure a real  izable and prac- 
t i c a l  pump design. 
TECHN l CAL D l  SCUSS l ON 
The mechanisms o f  erosion and abrasion wear, and i t s  r e l a t i o n  t o  ve loc i t y  
and mater ia l  wear resistance, i s  now discussed i n  order t o  present an under- 
standing of the phenomenon and the design problems i t  presents. Both hydro- 
dynamic and mechanical design considerations are discussed where abrasion 
cont ro l  can be exercised through cont ro l  o f  pump in te rna l  flow ve loc i t i es ,  
simple geometry, and generous and continuous bends and curvatures. The e f -  
f ec t  of pump design parameters on pump in te rna l  r e l a t i v e  v e l o c i t i e s  i s  
b r i e f l y  described. A discussion o f  promising pump mater ia ls ,  o f  construct ion, 
and hard facing coatings and inser ts  i s  a lso presented. 
PUMP ABRASION AND EROSION 
Figure 1 i l l u s t r a t e s  c r i t i c a l  areas i n  a cen t r i f uga l  pump where abrasion 
and impact erosion wear problems may be expected. These include -$rasion on 
impel ler f r o n t  shroud and back p la te ,  casing and volute, wear r i  ~ n d  seals; 
and erosion o f  impel ler  blade leading and t r a i l i n g  edges and the v o l ~ t e  cut-  
water. Although p a r t i c l e  s ize  and shape are factors a f fec t ing  wear, general ly 
abrasive wear i n  s l u r r i e s  i s  found t o  vary as the 2.7 power of  s l u r r y  ve loc i t y .  
Thus, i f  s l u r r y  f low ve loc i t y  i s  doubled, the erosion wear r a t e  i s  increased 
s i x fo ld .  I n  an optimum s l u r r y  pbmp design, therefore, loca l  s l u r r y  ve loc i -  
t i e s  r e l a t i v e  t o  metal surfaces must be kept low t o  reduce abrasion and high- 
ve loc i t y  impingement against metal surfaces. Also, i n  appropriate pa r t s  o f  
the pump, h igh hardness mater ia l  and coating should be used t o  reduce abra- 
s ive  wear and d u c t i l e  mater ia ls  may be used to  reduce impact erosive wear. 
Y VOLUTE YliLLS ABRASION 
77-5 5 
TMILING-EDGE EROSION 
CUTUATER I W 1  
IMPELLER snaouo 
SLURRY C W A C T l r n  
MAR rlm AMASION 
SEAL A D M S l O l  
I 
- \ 
Figure 1. C r i t i c a l  Areas o f  Wear i n  a Cent r i fuga l  Pump 
Despite the h i gh  pump t i p  speed needed t o  develop h i gh  pressures i n  a minimum 
number of  stages, an understanding of  the s l u r r y  wear problems w i l l  enable 
the designer t o  mainta in  law loca l  s l u r r y  v e l o c i t i e s  near metal surfaces t o  
ensure maximum pump opera t ing  l i f e .  
HVDRAUL l C DES l GN 
The maximum r e l a t i v e  v e l o c i t i e s  t ha t  occur i n  pumps a re  t t  the impe l le r  i n l e t  
eye, a t  the impe l le r  e x i t ,  and a t  the vo l1 .e  cutwater.  Typ ica l  v e l o c i t i e s  
as a f unc t i on  o f  pump parameters f low c o e f f i c i e n t  ($) and head c o e f f i c i e n t  
($) a re  shown i n  Figures 2 and 3. The impe l le r  i n l e t  r e l a t i v e  v e l o c i t y  can 
be minimized by reducing the i n l e t  eye diameter o r  by in t roduc ing  i n l e t  w h i r l  
i n  the d i r e c t i o n  o f  r o t a t i o n .  Using impe l le r  i n l e t  w h i r l  i s  des i rab le  s ince 
i t  reduces in te rs tage  d i f f u s i o n  requirements i n  a mu l t i s tage  pump (as the d i f -  
fuser i s  no t  requi red t o  remove a l l  the w h i r l  v e l o c i t y )  and permi ts  a l l  im- 
p e l l e r s  t o  be hydrodynamically i d e n t i c a l .  
The impel ler  design af fects  e f f i c i ency  d i r e c t l y .  The nuvber of blades, en- 
t rance angle t o  the blades, blade thickness and blade contour a re  a l l  p e r t i -  
nent design lements. S l u r r y  f low v e l o c i t i e s  are a l s o  d i r e c t l y  r e l a ted  t o  
ORIGNAL PAGE 6 
OF POOR Q U A W  
Figure 2. E f fec t  o f  Pump Design Figure 3. Ef fect  of Pump Head 
Parameters on Pump Coef f i c ien t  on Volute 
Relat ive Ve loc i t ies  I n l e t  Relat ive Veloc i ty  
these same design elements. Thus, if an impel ler  i s  designed f o r  large flow 
passage areas by using fewer and th icker  blades t o  reduce s l u r r y  ve loc i t y ,  
i t  must be traded o f f  w i t h  possible f l c u  separation and eddies, causing loca l -  
ized wear, and loss i n  hydraul ic  e f f i c i ency  that  may resu l t .  
Impel ler f ron t  shroud and back p l a t e  clearances can be used t o  cont ro l  i n t e r -  
nal v e l o c i t i e s  and close-clearance abrasion t o  some extent.  Increasing the 
c lea rancs  w i l l  minimize po ten t i a l  abrasion wear problems; however, t h i s  must 
be evaluated against r;duced e f f i c iency ,  induced r e c i r c u l a t i o n  w i t h i n  the 
clearances, and secondary flows from high t o  low pressure areas. Secondary 
flows themselves w i l l  cause loca l ized erosion. Using impel ler wear r i ngs  i s  
a  l i m i t e d  so lu t ion  t o  t h i s  problem. 
As h igh  s l u r r y  v e l c c i t y  occurs a t  the impe l le r  e x i t  o r  vo lu te  i n l e t ,  increas- 
i ng  the cutwater clearance a t  the vo lu te  tongue w i l l  reduce s l u r r y  v e l o c i t y  
and impact erosion. However, loss iti e f f i c i ency  must be minimized. Operation 
o f  the pump a t  p a r t i a l  capac i ty  (low f lw cond i t ions)  must a l s o  be kppt a t  a 
minimum, as accentuated "off-design impingement angle" w i l l  cause h igh  impact 
eros ion a t  the impe l le r  blade and vo lu te  cutwater.  
WEAR MECHANISM 
Erosion o f  a surface by s o l i d  p a r t i c l e s  en t ra ined  i n  a f l u i d  stream i s  ob- 
served i n  many d i f f e r e n t  app l i ca t ions  such as coal-burning tu rb ines ,  coal  
hydrogenation process equipment, coal  t ranspor t  p ipe l ines ,  suc t ion  dredges, 
and coal-burping, furnace-induced fans. I n  the present a p p l i c a t i o n  of a 
s l u r r y  pump f o r  a coal  l i q u e f a c t i o n  process, the s o l i d s  concentrat ion by 
weight w i l l  be as h igh as 50 percent. I n  the study o f  the wear phenomenon 
i n  the pump design, t h i s  h igh concentrat ion o f  s o l i d s  a t  h igh  v e l o c i t i e s  must 
be care fu l  l y  considered. 
The two bas ic  types o f  wear mechanisns t ha t  occur i n  a f l u i d  stream conta in ing 
s o l i d  p a r t i c l e s  are: d u c t i l e  eros ion (abrasion),  and b r i t t l e  eros ion ( impact) .  
The former type i s  one i n  which the mater ia l  removal i s  due e n t i r e l y  t o  the 
c u t t i n g  o r  d i sp lac ing  a c t i o n  o f  the p a r t i c l e ,  s i m i l a r  t o  g r i n d i n g  o r  s i ng le -  
t o o l  c u t t i n g  processes; the l a t t e r  type i s  one i n  hh i ch  the removal of  surface 
ma te r i a l  i s  caused by a stream o f  impinging s o l i d  p a r t i c l e s  as I n  sandblast-  
ing, o r  by l i q u i d  impact, as i n  the case o f  i tnpel ler  cav i t a t i on .  
The mechanical p rope r t i es  invo lved i n  the eros ion rr~chanism between the s o l i d  
p a r t i c l e s  and mater ia l  sur face include: hardness, p l a s t i c  f low s t ress ,  and 
Young's modulus. The s l u r r y  p roper t ies  invo lved are:  f l u i d  c a r r i e r ,  con- 
cen t ra t ion .  ve loc: ty ,  impingement angle, and p a r t i c l e  = I ze  d i s t r i b u t i o n ,  
shape, and r o t a t i o n .  
Abrasion 
The e ros i ve  c u t t i n g  of  d u c t i l e  mater ia ls  has been s tud ied a n a l y t i c a l l y  by 
F inn ie  (Ref. 1). The ana lys is  e s s e n t i a l l y  invo lves the s o l u t i o n  o f  the 
equations o f  motion o f  the p a r t i c l e  i n t o  'he eroded mater ia l  under the ac t ion  
o f  the r e s i s t i n g  p l a s t i c  f lw st ress  o f  the mater ia l .  The amount of mater ia l  
the p a r t i c l e  removes i s  then determined from the displacement path of par- 
t i c l e  I n  the mater ia l .  From analyses, the fo l lowing re la t ionsh ip  i s  obtained 
for the volume o f  mater ia l  removed by pa r t i c l es :  
MV' 1 Q = C -  - f  (a) 2 P 
where 
Q = volume o f  mater ia l  removed 
M = masso f  imp lng ingpar t i c l es  
V = p a r t i c l e  Impinging ve loc i t y  
P = p l a s t i c  f l a w  s t ress 
f (a)  = a funct ion o f  impinging angle a t o  the eroding surface 
C = a constant ranging 1/8 t o  1/12 
Equation (1) indicates tha t  f o r  the 
erosion o f  d u c t i l e  mater ia ls  o r  
abrasion, the mater ia l  removal 
. . .  
- 
varies l i n e a r l y  w i t h  the t o t a l  quan- mm16' - ALUMINUM 
0 ALUMINUM  OX^# - 
t i t y  of  the impinging p a r t i c l e s  and - W 
- 
t o  the square of the impinging vel -  
oc i  t: and i s  independent o f  the 
- 
p a r t i c l e  size. The only  mater ia l  
property tha t  af fects the erosion i s  
the p l a s t i c  f lw stress p. I t  a lso  
var ies as a funct ion o f  impinging 
angle as shown by the dotted curve 
f o r  aluminum a l l o y  i n  Figure 4. 
ANGLE O f  IMPINGEYENT, e* The va r ia t i on  o f  the erosion c f  duc- 
t i l e  mater ia l  w i t h  impinging angle a 
Figure 4. Erosion o f  Aluminum 
can be explained as fol lows. A t  and Hish-Density Aluminum 
s r 3 l l  values o f  a, erosion increases oxid; by S i c  Pa r t i c l es  (120 Mesh and 500 f t /sec) 
w i t h  a due t o  increas ing normal v e l o c i t y  component and r e s u l t i n g  i n  increas- 
ing  f o r ce  o f  pene t ra t i on  i n t o  the ma te r i a l  by the p a r t i c l e .  A t  l a rge  values 
o f  a, the forward c u t t i n g  v e l o c i t y  component decreases w i t h  a, r e s u l t i n g  i n  
decreasing forward displacement and erosion. The maximum ma te r i a l  removal 
can be seen t o  occur a t  an impinging angle o f  approximately 20 degrees. The 
a n a l y t i c a l  r e l a t i o n s h i p ,  however, underestimates the ma te r i a l  removai a t  
la rge angles as ind ica ted  by the s o l i d  curve obta ined exper imenta l ly .  The 
dev ia t i on  i s  a t t r i b u t e d  genera l l y  t o  the sur face roughing and work hardening 
by the impinging p a r t i c l e s  a t  l a rge  angles. 
E ros ion  
The study o f  e ros ion  f o r  b r i t t l e  ma te r i a l s  has been made by Sheldon and 
F inn ie  ( ~ e f .  2 ) .  The ana lys is  app l i es  the c l a s s i c a l  Her tz  equations t o  de- 
r i v e  the deptn o f  pene t ra t ion  and the r e s u l t i n g  s t resses i n  the reg ion around 
the  ma te r i a l  i nden ta t ion  and then fo l lowed the  Weibul l  theory o f  mean f rac-  
t u re  s t r eng th  o f  a ma te r i a l  w i t h  a volume d i s t r i b u t i o n  o f  f laws t o  determine 
the volume o f  f r a c t u r e  f o r  an impinging angle o f  90 degrees. The f o l l o w i n g  
9 r e l a t i o n s h i p  f o r  weight removal i n  cub ic  cent imeter  per 10 p a r t i c l e s  was 
obtained: 
where 
9 W = weight removal per 10 p a r t i c l e s  
R = m e a n p a r t i c l e r a d i u s  
V = impinging v e l o c i t y  w i t h  a = 90 degrees 
K = e ros ion  parameter i n  cc per l o9  abras ive p a r t i c l e s  
a, b = exponents dependent on ma te r i a l s  and shape o f  p a r t i c l e s  
The eros ion weight loss on b r i t t l e  ma te r i a l s  i s  dependent on p a r t i c l e  s i z e  
and i s  a f unc t i on  o f  l a rge r  power o f  the v e l o c i t y  t11an the weight loss or; duc- 
t i l e  ma te r i a l .  The v a r i a t i o n  o f  b r i t t l e  ma te r i a l  e ros ion  w i t h  impinging 
angle i s  shown by the  s o l i d  curve f o r  aluminum ox ide i n  F igure 4. Exper i -  
mental r e s u l t s  i nd i ca te  the s i ze  exponent (a) can vary frm 3 t o  5 and the 
v e l o c i t y  exponent (b) i s  c lose  t o  2.7. 
CAND 1 DATE WTER l ALS 
The optimum s l u r r y  pump may be comprised of both d u c t i l e  and b r i t t l e  mater ia ls ,  
w i t h  the l a t t e r  used i n  se lected high-wear areas where impingement angles are 
low. Since hardness I s  o f t en  a des i rab le  proper ty  i n  low-impingement areas 
where wear can be a problem, the l i s t  o f  candidates w i l l  r e f l e c t  most ly 
mater ia ls  of  h i gh  hardness. P r o d u c i b i l i t y  i s  another major f ac to r  which must 
be considered f o r  eny l i s t  o f  mate r ia ls ,  w i t h  cas t ing ,  plasma-spraying, pack 
o r  vapor-di f fusion processes, welding, braz ing,  and mechanical j o i n i n g  as pos- 
s i b l e  f a b r i c a t i o n  methods. 
PROGRAM STATUS 
A complete engineer ing study i s  being made on several p o t e n t i a l  concepts f o r  
the high-pressure, high-capaci ty,  mu l t i s tage  cen t r i f uga l  pump fo r  c o a l / o i l  
s l u r r y .  Th is  study i s  f u r t h e r  supported by op t im i za t i on  ana lys is  and exper i -  
mental eva lua t ion  of  wear-ve loc i ty  r e l a t i onsh ips .  De ta i led  design layouts 
are being made such t ha t :  component hyd rau l i c  design; s t r u c t u r a l  s t ress ;  
c r i t i c a l  speed dynamics; t h rus t ,  seals and bear ing loads; and ma te r i a l  
processes can a l l  be p roper ly  evaluated. 
The hydrbu l i c  design of  pump i n t e r n a l s  emphasizes optimum v e l o c i t y  d i s t r i b u -  
t i o n s  and minimum h i g h l y  l oca l i zed  v e l o c i t i e s .  Generous f low rad ius o f  curva- 
t u r e  i s  used and abrupt surface d i s c o n t i n u i t y  i s  avoided. The mechanical 
design o f  the pump u t i l i z e s  the most appropr ia te  wear- res is tant  ma te r i a l s ,  and 
i s  conf igured f o r  s imple f a b r i c a t i o n  and assembly. Slnce abrasive and ero- 
s i ve  wear eventual ly  occurs, the pump design a l s o  incorporates convenient 
dissssembly f o r  inspect ion and p a r t s  replacement dur ing  minor maintenance and 
f i n a l  overhaul . 
77-55 
TABLE 1 .  POTENTIAL PUMP MATERIALS 
- 
Mate r i a l  
D u c t i l e :  
S ta in less  Stee l  ( C A ~ N H )  
Cast Stee l  (ASTM216) 
T i tan ium (c.P.) 
---- 
Hardness (DPH) 
(~pp rox ima te )  
320 
2  50 
250 
B r i t t l e :  I I 
Ni-Hard Cast I r o n  
400C Stee l  
Manganese S tee 1 
White Cast I r o n  
Coatings 6 I nse r t s  
S i l i c o n  Carbide 
S i l i c o n  N i t r i d e  
Tungsten Carbi de 
Alumina 
T i r ba loy  T-800 
S te l  1  i t e  (1016) 
650 
650 
580 
500 
3000 
3000 
2100 
2000 
700 
650 
I 
REFERENCES 
1 .  F inn ic ,  I .  - "Erosion o f  Surfaces by Sol id  Par t ic les ,"  Weat., Vol .  3 ,  
1960, p. 87. 
2 .  Sheldon, G .  L . ,  and I .  F innic  - "The Mechanism o f  Mater ia l  Removal i n  
the Erosive Cutt ing o f  B r i t t l e  Mater ia ls , "  Journal o f  Engineering for 
I ndustry , Trans. ASME, Vol . 88, 1966. 


Rocketdyne's advanced coal slurry pumping program

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