How clean gas is made from coal Here are the operating experience and some preliminary results f r o m a fluidized-bed pilot plant built to show what needs to be removed and how to do it R. M. Felder R. M. Kelly J. K. Ferrell
R. W. Rousseau Department of Chemical Engineering N o r t h Carolina S t a t e Uniuersity Raleigh, N . C . 27650
Many of the factors currently limiting the large-scale development of coal conversion technology are environmental in nature. Many processes to gasify coal exist, and some are available commercially, but the technology of synthesis gas cleanup is not as well developed. Moreover, the total
Project objective The overall objective of the project is to characterize completely the gaseous and condensed-phase emissions from the gasification-gascleaning process, and to determine how emission rates of various pollutants and methanation catalyst poisons depend on adjustable process parameters. Specific tasks to be performed are as follows: Identify and measure the gross and trace species concentrations in the gasifier product, including concentrations of sulfur gases (H&, COS); organics (such as benzene, toluene and xylene, and polynuclear aromatic hydrocarbons); water-soluble species (for example, ammonia, cyanates, cyanides, halides, phenols, sulfates, sulfides, sulfites, and thiocyanates); and trace metals (antimony, arsenic, beryllium, bismuth, cadmium, lead, mercury, selenium, and vanadium).
658
Environmental Science & Technology
environmental impact of the widespread implementation of gasification technology is not yet understood. Recognizing this problem, the Environmental Protection Agency (EPA), in 1977, contracted for the design and construction of a pilot-plant coal gasification-gas-cleaning test facility at North Carolina State University, to be operated by the faculty and staff of the Department of Chemical Engineering. Construction began in January 1978 and was completed and turned over to the university in the summer of 1978. Details of the plant facilities and operating procedures may be found in a recent EPA technical report (Ferrell et al., EPA-600/7-80-046a, March 1980). This paper presents a brief de-
* Correlate measured emission levels with coal composition and gasifier operating variables, particularly temperature, pressure, and solid and gas-phase residence time distributions. Perform material balances around the gasifier, the raw gas cleanup system, and the acid gas removal system, and determine the extent to which selected species are removed from the synthesis gas in each of the subsystems. Corretate measured extents of conversion and removal efficiencies for various species with system operating variables, including temperatures, pressures, holdup times, and solvent circulation rates. Evaluate and compare the performance characteristics of alternative acid gas removal processes, considering both C02 and H2S removal capabilities and the degrees to which
scription of the plant and illustrates the kinds of data that the plant is capable of producing. The principal components of the pilot plant are a continuous fluidizedbed gasifier, a cyclone separator, and a venturi scrubber for removing particles, condensables, and water-soluble species from the raw synthesis gas. There are also absorption and stripping towers, as well as a flash tank for acid-gas removal and solvent regeneration. The gasifier operates at pressures up to 800 kPa ( 1 00 psig), has a capacity of 23 kg coal/h (50 Ib/h), and runs with either steam-air or steamoxygen feed mixtures. The acid gas removal system is modular in design, so that alternative absorption processes may be evaluated.
the processes remove trace pollutant species from the sour synthesis gas; and evaluate the buildup of contaminates in the various acid gas removal solvents. Use the results obtained in the atiove studies to develop models for the gasification and the gas cleanup processes. The models will take 8s input variables the composition and feed rate of the coal, bed depth, steam and air (or oxygen) feed rates and inlet temperatures, gasifier pressure, and operating conditions (temperatures, pressures, solvent flow rates) for the gas-cleaningsystems, and will predict the coal conversion and the product gas flow rate and composition, including trace pollutant levels. The model will be used as a basis for optimizing the pilot-plant operating conditions, and for estimating emission levels for scaled-up versions of the processes investigated.
0013-936X/80/0914-0658$01 .OO/O @ 1980 American Chemical Society
FIGURE 1
Utilities system
Gasifier
I
HzS
Preheater Manifold
FIC = Flow indicator and controller TIC = Temperature indicator and controller S = Sample port
Superheater Steam
M Bypass drain
Calibrate
FIGURE 2
Gasifier- PCS system NZ Purge
Cyclone Venturi scrubber
PIC = Pressure indicator and controller S = Sample port Gasifier
? NZ purge
Heat exchangers
Char receiver
NZ purge
Circulation pump AGRS
Nz 0 2
Steam Plant water
M
w
Drain
Volume 14, Number 6, June 1980 659
Associated with the plant are facilities for direct digital control of all process systems. and on-line data acquisition, logging, and graphic display. Facilities for sampling and exhaustive chemical analysis of all solid, liquid, and gaseous feed and effluent streams a r e also available. The pilot plant consists of six subsystems: gasifier, coal feed, and char removal sjstem particles, condensables, and solubles removal (PCS, or raw-gas cleaning) system acid gas removal system ( A G RS) utilities system instrumentation and process control sjstem data acquisition and display system. The gasifier The gasifier (Figures 1 and 2) is a 15.2-cm (6-in) I.D. Schedule 40 pipe (3 16 SS) enclosed in several lajers of insulation and is contained in a 61-cm (24-in.) I.D. Schedule 80 carbon steel pipe. The overall height of the unit is roughlq 3.7 m ( I2 ft). Thermocouples are mounted in the center of the bed a t six positions above the gasifier feed cones to monitor the bed temperature profile. Differential pressure taps are (FIGURE
set a t 5.9 cm and 13.8 cm ( 1 5 i n . and 35 in.) above the feed cones, and the pressure drop between the taps is used as an operating parameter. The cones are three 12.7-mm-diameter (0.5-in.) tubes arranged triangularly, with each tube tapering out to 2.5 c m ( 1 in.) for better flow distribution. Coal is fed and removed by screw conveyers from pressurized hoppers a t either end of the vertical reactor. T h e bed height may be 1-1.3 m (38-52 in.). The level of the fluidized bed is monitored with a nuclear-level gauge and is kept constant by adjusting the char removal screw rotation rate. The coal feed and removal systems contain nitrogen purges to prevent backflushing of any reactants. The insulation section around the gasifier is also equipped with a nitrogen purge flow for safety considerations. The gasifier typically operates a t 790 kPa (IO0 psig) and 1150-1310 K (1600-1900 OF). The principal reaction is that of steam and carbon to form CO and Hz: combustion of carbon also occurs. Carbon conversions on the order of 30-70% have been obtained in preliminary runs. The PCS system The raw gas produced in the gasifier is fed to the PCS subsystem (Figure 2). A cyclone separator removes most
particles, and a venturi scrubber quenches the gas stream, removing water-soluble and condensable compounds a t the same time. T h e quenched gas stream is fed through a shell and tube heat exchanger to a condensate receiving tank. Water in the receiving tank can be discarded or recirculated to the venturi scrubber. The gas leaving the tank goes through a second heat exchanger to a mist eliminator, and then through either a coalescing or a cartridge filter. The pressure drop around the filter is monitored: if plugging is observed, the flow is directed to a parallel filter while the first is cleaned or replaced. After leaving the filter, the sour gas is either burned in a shielded flare located on the roof or fed to the acid gas removal system. Acid gas remokal system The acid gas removal sjstem (Figure 3) is designed to r u n in four different modes. These include operation with refrigerated methanol. hot potassium carbonate, monoethanolamine, and dimethyl ether of polyethylene glycol. All experience to date has been with methanol, so onlj this mode of operation hill be described. The A G R S can accept either a sour-gas feed stream from the gasifier or a synthetic-gas (syngas) feed
3
Acid gas removal system (AGRS) Syn gas Sour gas
Dehydrator
compressor Heater
N2
FIC PIC TIC
Flow indicator and controller
=
Pressure indicator and controller Temperature indicator and controller Sample port
=
( s=
660
4
=
Environmental Science & Technology
chiller
Solvent Pump
stream. The feed gas is first passed through a dehydrator, then compressed to 3.54 MPa (500 psig), cooled, and fed to an absorption column. The absorber contains approximately 6.5 m (21.5 ft) of 6.4-mm ('/4-in.) ceramic lntalox saddles. The 12.7-cm-diameter (5-in.) column can accept solvent feed at any of three locations, providing flexibility for mass-transfer studies. The sweet gas (whatever remains after CO2, H*S, and other sulfur gases are absorbed) is then burned in the shielded flare. The recirculating methanol is refrigerated to about 240 K (-30 OF) before being routed to the absorber. After passing through the absorber, the methanol is sent to a flash tank to reduce its pressure to about 790 kPa ( 100 psig). The 15.2-cm-diameter (6-in.) stripping column, containing 6.9 m (22.5 ft) of ceramic Intalox saddles, is operated a t about 170 kPa (IO psig), with nitrogen used as the stripping gas. The column feed temperature can be regulated by a trim heater. The solvent is regenerated and sent through a gas chiller (to cool the entering sour gas further) before being sent to the refrigeration unit to u n dergo another cycle. Both the gasifier and A G R S are linked to the utilities subsystem (Figure I ) , which provides the feed streams to both systems. Nitrogen, oxygen (or air), and steam are all regulated through flow control loops to the gasifier, while a prepared mixture o f N2. CO2, HpS, and other gases can be fed to the A G R S in place of gasifier make gas. The feed stream to the gasifier is first preheated (Nz, (&/air) or superheated (steam). The syngas feed to the AGRS is mixed and regulated through a flow control valve on the sour-gas compressor outlet. Plant operation is monitored and regulated from a control room. Signals from 96 sensors (temperature, pressure, flow rate, and the like) are sent to a control panel, where they are processed and sent to a video display terminal, a Honeywell T D C 2000 process control computer, and a PDP-I 1 / 34-based plant data acquisition system. The T D C 2000 regulates 16 different control loops in the plant. An alarm panel superimposed on a process schematic provides visual and auditory indications of potentially hazardous conditions. Solid, liquid, and gas samples from the pilot plant are analyzed in four analytical laboratories. Table 1 lists compounds and major, minor, and trace elements that are analyzed. Samples are drawn for analysis at the sample point locations shown on
TABLE 1
Coal gasification analytical program Sample type
CoaVchar
Analysis
Proxlmate Ultimate Trace element
Gas/solvents
Compounds Trace elements
Wastewater
Major elements Compounds
Trace elements
Analyte
Sieve analysis, density, free swelling index Moisture, ash, volatile matter, fixed carbon C, H, N, 0,S As, Be, Cd, Cr, Hg, Ni, Pb, Sb, V N2, CO, COP,H2, H20, CH30H, CH4, H2S, COS, CS2, mercaptans As, Be, Cd, Cr, Hg, Ni, Pb, Sb, V
C,N, S Ammonia, total organic carbon, chloride, COD, cyanate, cyanide, pH, phenolics, residue, sulfate, sulfide, sulfite, thiocyanate, benzene, toluene, xylene As, Be, Cd, Cr, Hg, Ni, Pb, Sb, V
the plant schematics (Figures 2 and 3). All gas samples are taken in heated 1 - L sample cylinders. Raw-gas samples at 790 kPa (100 psig) are drawn from the cylone and PCS system exits. Also available are high- and lowpressure samples of cleaned and cooled gas drawn from a sampling train at the cyclone exit. I n addition to providing a clean gas sample, the sampling train allows for a gravimetric determination of the water content of the gasifier effluent and provides liquid samples that may be analyzed for condensable and soluble species in the effluent. Integrated liquid samples can also be taken from the receiving tank following the venturi scrubber. Whenever they are obtained, liquid samples a r e immediately subjected to appropriate preservation steps and are stored to await subsequent analysis. Illustrative results: gasifier Gasifier run GO-48 was made on Feb. 26, 1980 and consisted of the steam-oxygen gasification of pretreated Western Kentucky # 1 1 bituminous coal of I O X 80 mesh size. Only the gasifier and PCS system were used; other runs have been carried out in which the gasifier and acid gas removal systems were integrated. The raw plant and chemical analysis data were processed to generate input for a data-logging and material- and energy-balance program. A portion of of the program output is shown in Figure 4. Figure 4 contains a graphical summary of the run, in which key variables presented in the detailed output are displayed. As the chart shows, coal
(more precisely, coke) was fed at an average rate of 15.7 kg/h (34.5 Ib/h) and spent char was removed at 7.2 kg/h ( I 5.9 Ib/h), representing (after elutriated dust had been accounted for) a conversion of about 54% on a total mass basis. The temperature in the reactor varied from I287 K ( 1867 O F ) 5 in. above the feed cone to 1248 K ( 1 787 OF) 35 in. above the cones. The bed height was 97 cm (38 in.) '1 bove the cones, so that the temperatures at the higher points (45 in. and 55 in.) did not reflect temperatures within the bed. The gas feed composition is shown below the gasifier. The molar steam to carbon ratio was close to 1 :3. A small amount of nitrogen was included in the feed mixture to control the superficial gas velocity. The average bed temperature and pressure were 1272 K (1830 O F ) and 817 kPa (104 psig) respectively. The carbon conversion in the reactor, determined as the total molar flow rate of carbon in the make gas divided by the feed rate of carbon, equaled 55%, and the make gas flow rate (after water has been condensed) was 2.3 kmol/h (16.4 scfm). The make gas contained 20.2% C O , 28.8% H2, and 0.6% CH4. The paragraphs that follow summarize the results and the calculations used to generate them. They are more or less in the order in which the results appear on the computer output, also shown in Figure 4. In addition, several parameters used for subsequent correlation analysis are summarized in Figure 4. They include the solid holdup (7.4 kg, 16 Ib), estimated as the apparent solids density in Volume 14, Number 6 , June 1980
661
FIGURE 4
Fluidized-bed coal gasification reactor .
..
RUN NO. 60-48, 2/26/80, 11100 A.M.-3:30 P.M. COAL FEED, 34.5 LB/H
.- - - - - - 0.8134 C 0.0016 H 0.0456 0
;:;;;; E
.y
** ** * * ** *.-,----* * * * * *+
GAS OUTPUT
---I----
1 'I I
I T=1170°F 46.6% Hz0
******** G
0.1114ASH
~
~
~
l
** PROFILE E ** 55 IN. 1678 "F** * E 4 5 IN. 1772 * * ** 25 IN.
SCRUB
p
24.0 GPH GASIFIER
OF*
1799
SOLID HOLDUP = 16.3 LB
C CONVERSION = 54.7%
*********
'
CHAR REMOVAL
I
--------
I GAS FEED I+
0.7877 C 0.0036 H 0.0255 0 0.0050 N 0.0168 S 0.1615 ASH
I I I
r------
I ** * * * * * ** I +
56.0 LB/H Hz0 2.58 SCFM 02 1.47 SCFM Nz
** * I * T = 68 "F * I * * I V = 171 GAL I * * * ** * * * * * ***
24.1% 29.5% 2.0% 20.2% 23.3% 0.3%
co
Hz CH4 c02 N2 H20
7067 287 PPM HzS PPM COS
PCS TANK T P V (AV)
~
16.4 SCFM 65.9 "F 98.8 PSlG
'E I *
5 IN. 1867 "F:
15.9 LB/H +-------
OF
SOURGAS
10 IN. 1830 "F:
E
~
)I(VENTURI SCRUBBER I DP = 35.5 IN. H20 I T(ouT) = 205
I I I
CYCLONE
= TEMPERATURE = PRESSURE = VOLUME
= AVERAGE
1.33 MOL HzO/MOL C 0.57 MOL NdMOL 0 2
.. . and its data output CONTROL VARIABLES
OUTPUT VARIABLES = 1830.2 "F
TEMPERATURE Nd02 MOLAR FEED RATIO STEAM PARTIAL PRESSURE BED HEIGHT SOLID SPACE TIME GAS SPACE TIME
= = = =
= 8.5 IN. H20 (0.306 PSI) = 2.1 KPA
PRESSURE DROP OVER 20 IN.
0.57 97.27 PSI 3.17 FT 28.3 MIN 2.84 S
=
PCS GAS FLOW RATE CYCLONE GAS FLOW RATE
= 2.32 KMOUH
SOLID HOLDUP PRODUCT FUEL PROPERTIES
CONVERSION VARIABLES
28.9% MOLAR BASIS 0.608 l e co PRODUdED/LB COAL (MAF) 35.4% MOLAR BASIS) 0.054 \B H2 PRODUCED/LB COAL (MAF) 2.4% (MOLAR BASIS 0.029 LB CH4 PRODdCEDILB COAL (MAF) HEATING VALUE OF MAKE GAS
CARBON CONVERSION = 54.7% STEAM CONVERSION = 23.9% SULFUR CONVERSION = 69.8% SOLID MATERIAL BALANCE
= 3926.4 BTUlLB = 245.5 BTU/SCF = 9125.1 KJlKG
HEATING VALUE OF SWEET GAS = 7684.2 BTU/LB = 327.9 BTU/SCF = 17858.6 KJ/KG CYCLONE EXIT-GAS ANALYSIS
CO H2 CH4 COz N2 HzS COS H20
%WET
%DRY
LB-MOUH
12.87 15.77 1.08 10.79 12.48 0.38 0.02 46.62
24.12 29.54 2.03 20.21 23.37 0.71 0.03
0.658 0.806 0.055 0.552 0.638 0.019 0.001 2.384
-
HzS = 7067.0 PPM DRY = 288.0 PPM I D R d
cos
662
= 16.3 LB (7.4 KG)
Environmental Science & Technology
COAL FED SPENT CHAR COLLECTED CYCLONE DUST COLLECTED COAL GASIFIED
= = = =
275.5 LB 143.0 LB = 51.9% OF FEED 18.5 LB = 6.7% OF FEED 114.0 LB = 41.4% OF FEED
SPENT CHAR REMOVAL RATE = 15.9 LB/H CHAR RATE FOR MASS BALANCE = 15.1 LB/H
ELEMENTAL MATERIAL BALANCES: FLOWS IN LB/H MASS
C
H
0
N
S
COAL GASES TOTAL INPUT
34.5 89.4 123.9
28.07 0.00 28.07
0.05 6.27 6.32
1.57 63.55 65.12
0.03 19.61 19.64
0.930 0.000 0.930
CHAR DUST GASES WASTEWATER TOTAL OUTPUT
15.9 2.1 106.8 0.0 124.7
12.54 1.61 15.20 0.00 29.36
0.06 0.01 6.69 0.00 6.76
0.41 0.07 66.34 0.00 66.82
0.08
0.00 17.87 0.00 17.95
0.267 0.026 0.644 0.000 0.937
% RECOVERY
1'00.6% 104.,6% 106.9%
102.6%
91.4%
100.7%
the cyclone-effluent gas with water and purge nitrogen subtracted. The sweet gas is the make gas with COz and sulfur gases removed. The carbon conversion in the gasifier is calculated as the mass flow rate of carbon in the product gases divided by the feed rate of carbon in the coal. A 55% carbon conversion was obtained in Run GO-48. The steam conversion was 24%. A solid material balance for the total time period of the run was obtained by weighing the total amounts of coal fed and spent char and cyclone dust collected, and determining the coal gasified by difference. The rate at which spent char is removed during the steady-state period (7.2 kg/h, 15.9 Ib/h) is determined from the known rotational speed of the screw conveyor and the total mass of spent char collected. Also shown on the output page is the char removal rate that would close the total mass balance on the gasifier.
the bed times the bed volume; the solid space time (28.3 min, solids holdup/ coal feed rate); and the gas space time (2.84 s, bed height/superficial gas velocity). Also shown are the measured pressure drop over a 51-cm (20.-in.) segment of the bed, the gas flow rate (corrected for leakage) measured following the PCS removal system, and the gas flow rate at the cyclone outlet (calculated from the PCS gas flow rate by assuming that the molar flow rate of dry gas is the same at the two points).
Solid material balance Most of the remaining quantities shown in Figure 4 are derived from a chromatographic analysis of the cyclone exit gas. The fuel properties of the make gas are first summarized: These include the molar percentages of carbon monoxide (29%), hydrogen ( 3 5 % ) , and methane (2.4%), and the heating values of the make gas and sweet gas. The make gas is defined as TABLE 2
Trap water and trace elemdnt analyses Run GO-15, April 3, 1979 Trap water: pH = 7.08 Species
CIs03*-
sop Sitotal)
Production rate in gasifier Wh
C(mg/L)
WJl
68.4 22.7 38.4 237.0
450 150 250 1550
g Producedfkg coal fed
9.9 x 1 04 '3.3 x 10-4 5.5 x 10-4 3.4 x 10-3
0.039 0.013 0.021 0.13
Trace element analysis: ppm Spent char
Element
Coal
As
9.6 6.8 69.6 0.1 1 32.3 11.9 0.78 44.0
Be Cr Hg Ni
Pb Sb
v
12.4 8.8 75.0 0.080 132.0 11.9
Cyclone dust
Wastewater
16.8
0.007
. 7.6
0.55 57.0
0.06
0.85 71.0
0.07
-
-
Trace element material balance: flows in Ib/h'X 1000 ,
Element
In Coal
Char
out
0.21 0.15 1.5 0.0024 0.71 0.26 0.017 0.96
0.17 0.12 1.05 0.0011 1.84 0.17 0.008 0.80
Dust
Water
Total
-
0.19 0.13 1.1 0.0012 1.9 0.21 0.009 0.86
% Recovery
~
As
Be Cr
Hg Ni Pb Sb
v
0.013 0.006 0.06
0.1 0.04 0.0007 0.06
-
89 86 73
50 270 81 50 90
Trace-element analysis Trap water condensate is generally analyzed for pH and concentrations of various ionic species; the latter analysis is performed using a sulfur analyzer and an ion chromatograph. Also, the feed coal, spent char, cyclone dust, and sample trap water are analyzed for various trace metals using atomic absorption spectrophotometry. These data were not available for Run GO-48 at the time of this writing, and so representative data from another run ((30-15, 4/3/79) are shown in Table 2. The material balance closures for all elements but nickel are reasonable; the abnormally large value obtained for nickel suggests that this element is entering the spent char from somewhere in the reactor-possibly by being leached out at the reactor walls. The low percentage recoveries of mercury and antimony suggest their volatilities. At the present time, sampling systems to trap these and other elements from the gaseous reactor effluent are being tested, with a view toward closing the balances. Wastewater analysis I n addition to the trap water analyses discussed previously, detailed analyses were performed on the water collected in the PCS receiving tank following the venturi scrubber. Samples were drawn a t the beginning and end of the steady-state period of the
-
72.0 0.076 120.0 4.8
A chromatographic analysis of the gases at the cyclone exit is shown on the output page. Also given is a material balance on major elements, in which C, H, 0, N, S, total mass, and percentage recoveries (output/input) are shown. The relatively poor closures of the hydrogen (107%) and nitrogen (9 1 %) balances are not typical of recent results; normally, all balances close to within &5%. A rough energy balance on the gasifier (not shown in Figure 4) indicates that the unit may be considered adiabatic.
'
run. All the chemical analyses were carried out successfully with the exception of fluoride, total organic carbon (TOC), and cadmium. Fluoride in the wastewater samples could not be detected reliably because of the interference caused by the addition of formaldehyde to preserve sulfite in the wastewater. T O C could not be determined because of equipment problems, and the cadmium electrodeless discharge lamp was burned out and could not be used for the analysis. The results of the wastewater analyses are shown in Table 3. In this table, Volume 14, Number 6 , June 1980 663
FIGURE 5
.
Column temperature profiles and mass balances.. RUN NUMBER A-M-24, SYNGAS, 3/6/80
ABSORBER
FLASH TANK
STRIPPER
P = 447.21 PSlG
P = 147.94 PSlG
P = 9.89 PSlG
1I
-
I -b FLASH
+SWEET GAS
I 0.58 SCFM
9.89 SCFM (65.27 "F)
(76.27
* * * I* * ** -+1 * 1xxxxxx 1 ;xxxxxx 1 * * * DP = 3.25 IN Hz0 1 *
--
I I
(48.61
OF)
O F 1
1-33.69
OF*
y
I"' I I I I I I
* *
-+* 6.31 "F** * * * * * * ******
* * *I* * ** * * * 1.46 "F *it * * 0.02 ** * * * * * * -0.83 "F ; * 3.74 "F * * * * * * * 3.86 "F ** *
0.71 GPM W* I (24.81 *
I
* xxxxxx * ** xxxxxx * * * * * * z-34.95
-
I
MEOH FLOW
6.26 SCFM (60.34 "F)
OF)
I
0.71 GPM (-36.28 "F)
SOURGAS ---14.82 SCFM
--+ACID GAS
I I
GAS
* * * * ** * * * 13.77 "F t * * + : * * **--* * * * ***** \
OF)
I I I I I I I I I I
OF
Y
- -1.09(75.00
STRIPPING Nz SCFM
: 3.51 *:
+*
OF)
* * 21.92 "F ,** * * * * ******
STREAM COMPOSITION (MOL Yo) SOUR GAS SWEET GAS FLASH GAS STRIP Nz ACID GAS ABSORBOTa FLASHBOTa STRIPBOTa
COS --MEOH H2 GO Nz CH4
31.240 0.000 0000
0.000
0.000 0.000 68.760 0.000
0.000 0.000
39.980
i.620
i.660
0 000
0.000 0.000 98.370 0.000
0.000 0.000 0.000
0.000
0 000
0.000
0.000 0.000
0.000 0.000
58.350 0.000
100.000
0.000
75.630
7.793
7.476
0.000 0.000
0.000 0.000
0.000 2.730 0.000
0.000 0.000 91.430
92.315 0.000
1oo.000
0.209 0.000
0.000 0.000
0.000
0.000
0.000 0.000
0.000
0.000
21.620
0.777
0.000
0.000 0.000 0.000
*CALCULATED MASS BALANCE (LB-MOUH)
0 UT
IN
SOUR GAS CO2 HzS
cos
MEOH Hz
co
Nz cH4
0.774 0.000
0.000 0.000 0.000 0.000
1.703 0.000
TOTAL 2.477 (LB-MOUH)
STRIP Nz SWEET GAS FLASH GAS ACID GAS TOTAL INb TOTAL OUTb Yo RECOVERY
0.000 0.000 0.000 0.000 0.000 0.000 0.182
0.000
0.000 0.000 0.000 0.027 0.000 0.000 1.626 0.000
0.182
1.653
0.002
0.791 0.000 0.000 0.029
0.774 0.000 0.000 0.000
0.000 0.057 0.000
0.226 0.000
0.000 1.885 0.000
1.046
2.659
0.039 0.000
0.000 ,
n ooo
0.097
o ooo 0.000
bMETHANOL-FREE BAS1S TOTAL METHANOL LOSS = 0.057 LB-MOUH = 0.268 GAUH
664
Environmental Science & Technology
0.000
0.830
0.000 0.000 0.000 0.000 1.909
107.269 0.000 0.000 0.000 0.000 0.000 101.245
2.739
102.998
0.000
0.000
"F
*
.. . and ACRS data C02 H2 s
DP = 0.66 IN. Hz0
0.000
TO ABSORBER- -b
TABLE 3
Summary of wastewater analysesa Anaiyte
Ammonia Carbon Chloride COD Cyanate Cyanide Fluoride Nitrogen
Method/ instrument
PH Phenolics Residue Sulfate Sulfide Sulfite Sulfur Thiocyanate TOC
SM No. 418 Dohrman TOC-50 Dionex System 10 Hach COD Reactor SM No. 413 J ASTM-D-2036 Dionex System 10 SM No. 421 Orion 901 SM NO. 510 A-C SM No. 208 A Dionex System 10 SM No. 428 D Dionex System 10 Dionex System 10 SM No. 413 K Dohrman TOC-50
vc
Dohrman TOC-50
PCS-NSS wastewater mg/L
PCS-ss wastewater mg/L
Sampling train-SS mg/L
65.92 f 1.24 147 f 4 16.27 f 0.09 551.4 f 25.7 10.08 f 1.40 0.81 f 0.04
78.48 f 0.20 256 f 18
-
17.47 f 0.09 556.7 f 1.0
68.35 f 7.25
9.72 f 0.20 1.17 f 0.03
-
-
91.46 f 0.70 5.55 f 0.00 0.31 f 0.02 0.45 f 0.13 48.57 18.5 f 0.1 46.80 f 1.81 212.76 1.51 f 0.21
80.68 f 0.84
105
f 14
5.67 f 0.00 0.30 f 0.03 0.24 f 0.05
7.08 f -
0.05
51.37 50.8 f 0.0
38.45 f 1.55 -
17.63 f 1.81 227.97 2.25 f 0.06
22.73 f 16.77 237.1 1 f 20.26
-
212
f 15
Run GO-15, April 3, 1979 SM = Standard method (APHA, AWWA, WPCF) a
the term NSS stands for nonsteady state and indicates a sample taken prior to the steady portion of the run. The term SS indicates a steady-state sample. p H , CI-, and S032- were determined accurately. Ammonia, nitrogen, and cyanate analysis data show good reproducibility. The extent of cyanate hydrolysis is unknown, but it is known that the Kjeldahl nitrogen method is not sensitive to several nitrogen species which are present in gasifier wastewater. The extent to which the nitrogen analyses may be in error is also unknown. The carbon content of the wastewater decreased with time during analysis, probably because C O and C 0 2 escaped from the samples. The total residue analysis is characterized by low reproducibility. All other wastewater analyses are subject to interference from chemical species which are present in a heavily polluted and complex sample such as gasifier wastewater. The extent of this problem and possible solutions have been studied; however, insufficient data have been obtained thus far to yield useful conclusions.
While the system is often run in the former mode, frequent runs are also made with syngas. Presented here are some data from a recent run (AM-24, 3/6/80) using a feed gas concentration of 3 1.6% CO2 and 68.4% N2. The goals of this run were to provide necessary information for mathematical modeling and to test the vapor-liquid equilibrium data used. In Run AM-24, the system was operated with a methanol circulation rate of 2.71 L/min (0.7 15 gpm). Only one of three available sections of packing in the absorber and all three packed sections in the stripper were used. A schematic flow chart of the steady-state operation of the A G R S generated by the project data logging program is shown in Figure 5 , as is material balance information. After this analysis had been performed, it was found that the gas chromatograph was slightly out of calibration, which appears to account for the small discrepancy in the component balances. Similar success in closing mass balances for integrated runs with gasifier feeds has also been achieved.
AGRS operation As noted previously, the acid gas removal system can be run in two different modes: feeding product gas from the gasifier feeding a syngas mixture.
Future plans A series of gasifier runs with pretreated bituminous coal feed is currently in its final stages, and reports are being prepared that summarize and model the results. These reports include correlations of carbon con-
version, make-gas production, and sulfur-gas and 'trace-element emissions with gasifier operating conditions, principally temperature and steamoxygen-carbon feed ratios. The acid gas removal system has been subjected to a series of runs with both syngas and gasifier make gas as feeds; a t the present time, masstransfer parameters are being determined and correlated with the absorber and stripper temperature and pressure and the gas and solvent flow rates. I n addition, the ability of the A G R S to remove sulfur gases other than H2S from the gasifier product is being determined. The development of mathematical models to correlate the performance of both the gasifier and the AGRS systems is being carried out i n parallel with all experimentation. Beginning this summer, a nondevolatilized subbituminous coal will be used as the feedstock to the gasifier, with refrigerated methanol still being used as the A G R S solvent. After several months of integrated plant operation, a new absorption process will be implemented and tested; the decision as to which process has not yet been made. Acknowledgment The pilot plant and the operations associated with it are funded by Environmental Protection Agency Grant R804811-02. Project personnel who V o l u m e 14, Number 6, June 1980
665
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have played an indispensable part in planning and operations include Craig McCue (sampling and data logging), Bill Willis (computer operations), Victor Agreda (design and analytical laboratory facilities), Gary Folsom (plant operations), Larry Hamel (trace-element analysis), Kwin Black (gas analysis), Kathy Steinsberger and Mary Minogue (solids and wastewater analysis), Corinne Trexler (sampling and data analysis), Terrie Cavanaugh (report preparation), and a number of excellent undergraduates who have aided in the development of plant and laboratory procedures.
Richard M. Felder ( 1 ) is professor of chemical engineering at N.C. State University ( N C S U ) .H e holds a B.Ch.E. f r o m the City College of New York and a Ph.D. in chemical engineering f r o m Princeton University. His interests on the gasifier project include reactor analysis and modeling, and sampling and analysis methodology. Robert M. Kelly ( r ) is the project engineer on the gasijiier project, and is also a candidate f o r a Ph.D. in chemical engineering at NCSU. H e holds a B.S. and M.S. in chemical engineeringfrom the University of Virginia.
James K, Ferrell ( I ) is Alcoa Professor and
head of the Department of Chemical Engineering at N C S U and is the overall coordinator o f t h e coal gasification research project. He has a B.S. and M.S. f r o m the University of Missouri and a Ph.D.,from NCSU.
R. W. Rousseau ( r ) is professor of chemical engineering at NCSU. His B.S.. M.S., and Ph.D. degrees were all obtained at Louisiana State University. He is involved in research and development on separation processes with particular emphasis on crystallization, distallation. absorptionstripping, and adsorption. 666
Environmental Science & Technology
