1. Installation and Testing of Gravimetric Tar Quantification System
Jackson Gardner
The Biomass Lab, University of California Davis, Davis CA 95616
Abstract: This project describes a new method for measuring the tar concentration in a biomass gasifier system.
This method includes the use of a pressure cooker and a single impinger of cool water and absolutely no solvent.
The intended pathway includes a short connection line directly from the gasifier to a pressure cooker, a pressure
cooker containing a stainless steel canister of fiberglass wool and 6 meters of Santoprene tubing submerged in
water at 105˚C, an impinger of water submerged in an ice bath, a vacuum pump, a rotameter, and a dry gas
meter. For the time being, the system must be tested to properly remove all tars from the gas before being
connected to the vacuum pump thus initially it will be connected to a second tar measurement system
immediately after the cool water impinger.
Introduction
Gas produced by biomass gasification inevitably creates condensable hydrocarbons (tars). Tars are known to
clog up various pathways through the gasifier system and are also known to be toxic, thus it is important to have an
efficient system to remove as much tar as possible. The current tar measurement system employed in the Biomass Lab
follows the IEA tar protocol in which a series of impingers of solvent (isopropyl alcohol) pull the tars out of the gas. The
tar is then separated from the solvent and measured; a tedious and difficult process.
This new system involves a much simpler method for measuring tars as it only requires a simple gravimetric
process. Gas is run through an electric pressure cooker filled with water, kept at 105˚C, with a stainless steel canister of
fiberglass wool and 6 meters of Santoprene tubing on the inside. The tubing and fiberglass wool serve to knock out tars
from the gas stream and can be easily detached, weighed, cleaned, and reattached to the pressure cooker system. By
maintaining a temperature above water’s boiling point, water will not condense along with the tars and will instead
condense in the cool water impinger. Fortunately, there is no solvent involved in the data collection procedure thus the
process is much cleaner and easier to perform than the current method.
The relevant methods and materials of this project are predicted to be adjusted as the project proceeds. For the
time being, the pressure cooker must be received and have parts fitted to its specific dimensions thus the listed parts are
subject to change. The system will draw gas directly out of the gasifier, after the primary scrubber, and will end at a
secondary tar measurement system (Lisa’s system) to ascertain that this system functions properly in removing tar from
gas streams. If the secondary system yields negligible amounts of tar, it can be concluded that the pressure cooker system
successfully removes tar and leaves exhaustible air. In that case, the system will be connected directly to a pump system
leading to an exhaust line. If the secondary measurement system yields significant quantities of tar, the pressure cooker
system will be adjusted accordingly.
Methods and Materials
Materials List
Number Description Supplier: Part Number Price
1 Outlet type 316 stainless steel yorlok tube fitting through
pressure cooker lid
McMaster: 5182K345 18.60
2 Inlet type 316 stainless steel yorlok tube fitting through
pressure cooker lid
McMaster: 5182K345 18.60
1
3. 18 2” stainless steel tube McMaster: 89995K168 23.60
Total
Assembly Diagrams
Pressure Cooker Assembly
As one can see through the supplier comparison, it is much more cost-effective to order parts from McMaster
rather than from Grainger. Once these parts are ordered and received, the first step will be welding in the two
swagelok fittings (1 and 2) into the lid. Next, stainless steel canister must have stainless steel tubing welded into
the cap (4) and the base (3). Additionally, stainless steel circle must be welded onto the bottom of the stainless
steel pipe (3) to seal it off. All other pieces are assembled by tightening into corresponding fittings via
wrenches.
Initial Plan
3
4. Final Plan
Experimental Plan
Initial Trials
Gas will be taken directly from the end point of the gasification run, at the same
point where tar is currently measured using the IEA tar protocol system. Initial trials will
require a great deal of establishing proper functionality of the apparatus. Areas that may
be sensitive to error include perfecting the temperature inside the pressure cooker, leaks
4
5. among joints, and proper cleaning of the interior components that come into contact with
tar.
To verify the temperature inside the pressure cooker corresponds to the desired
105˚C, thermocouple readings will be taken and observed consistently. If the temperature
is off, it shall be adjusted by trial and error until the thermocouple provides the proper
reading. To avoid leaks among joints, soapy water can be applied to each connection point
as air is pushed through to verify that no air is leaking out, indicated by the absence of
bubbles forming. This, of course, would occur by testing the lid and its connected
components with air flow separate from the pressure cooker base. If air isleaking out,
joints will be refitted with a different particular piece (depending on the error occurring).
To avoid imperfect cleaning, various cleaning agents will be tested in the process of
removing tars from the Santoprene tubing and stainless steel canister.
Proving Trials
Gas will be diverted into two paths just before reaching the current IEA impinger
system. One route will continue to the impingers while the other route will run through
the pressure cooker system. Tar will be measured in both systems via each system’s
standard operating procedure. End measurement results (mass of tar collected) from each
system will then be recorded and compared for each gasifier run taking place in the coming
Winter quarter.
Pressure Cooker Tar Measurement: Standard Operating Procedure*
The purpose of this standard operating procedure (SOP) is for use of the pressure cooker
apparatus designed to measure tar quantity as gas leaves the gasifier. This SOP is a
reminder of the steps necessary to run a sequence but does not replace training. You must
be trained on this apparatus before using it.
Preparation
1. Record the mass of a beaker, coil Santoprene tubing into the beaker and place in the
oven for 12 hours at 105˚C.
2. Removed tubing and store in a desiccator for 1-2 hours to acclimate tubing to room
temperature.
3. Place canister and its cap in the dessicator at the same time as the tubing.
4. Remove canister from dessicator, open the canister, fill with new fiberglass wool,
and replace cap.
5. Record the mass of the canister with fiberglass wool.
6. Fasten canister into the lid piece of the pressure cooker.
7. Remove Santoprene tubing from the desiccator.
5
6. 8. Record the mass of the tubing.
9. Connect tubing via compression fittings to the pipe piece and the previously
installed canister.
10. Fill the pressure cooker with water until the tubing and canister are completely
submerged.
11. Seal pressure cooker shut.
Measurement
12. Set the pressure cooker to boil water at 105˚C.
13. When 105˚C is reached, connect gas line from the gasifier to the inlet of the pressure
cooker.
14. Open valve to gas line to allow gas flow for the duration of the gasifier run.
15. Close gas line valve after gasifier run is complete.
16. Set the oven to maintain a 105˚C temperature.
17. Turn off pressure cooker. Allow it to cool for 20 minutes.
18. Record the mass of a tray.
19. Using insulated gloves, remove lid from pressure cooker and wipe down the canister
and tubing to remove moisture.
20. Unscrew compression fittings to release tubing and immediately clip both ends shut.
21. Place the tubing in the previously weighed tray and insert into the oven for 1 hour.
22. Unscrew the canister, with its lid still attached, and immediately weigh and record
the mass.
23. Remove tubing from the oven after the hour is up and record the mass of the tubing
+ tray.
Cleaning
24. Drain water from the pressure cooker.
25. Open the canister, remove the fiberglass wool and place it in the toxic solid waste
bag.
26. Wash and scrub the canister with soap.
27. Fill a large beaker halfway with soapy water, unclip one end of the Santoprene
tubing and submerge it into water.
28. Unclip and attach the other end of the Santoprene tubing to a pump.
29. Submerge additional tube from the other side of the pump into the soapy water.
30. Turn on pump to circulate soapy water and remove tars from the tubing.
31. Dispose of tar water in the toxic liquid waste container.
32. Turn off pump, disconnect tubing, and leave to dry.
*Xu, Ming, Robert C. Brown, Glenn Norton, and Jerod Smeenk. "Comparison of a Solvent-Free Tar Quantification
Method to the International Energy Agency’s Tar Measurement Protocol." Energy & Fuels(2015): 2509-513.
Web. 12 Oct. 2014.
6
7. Cited paper was used in constructing the preparation and measurement points of the standard
operating procedure.
Results and Discussion
Nozzle size
Under the conditions that the gasifier flow rate (Q_duct) after the scrubber is 200
L/min and the inner diameter of the duct is 1.61 inches, we can set a range of possible flow
rates leading to the pressure cooker system (Q_DGM) and determine the corresponding
inner diameter size of the nozzle (ID_nozzle) that draws out of the gasifier duct. Since the
temperature change is ideally negligible, it need not be accounted for in these calculations.
The remainder of this section shall be filled in over the coming weeks as the
installation process proceeds upon receiving parts.
Conclusions/Future Plans
For the time being, a great portion on the project relies on the dimensions of the
incoming pressure cooker. Since the most cost-effective pressure cookers can be
purchased through ebay, the most likely candidate for selection varies day by day. Upon
receiving the green light to order a pressure cooker, the most economical cooker capable of
these purposes will be purchased. When the pressure cooker is received, the remaining
parts will be tailored to its dimensions.
The first issue will be welding in the various components to the pressure cooker lid.
Many modern electric pressure cookers have a great deal of plastic on the lid, thus it must
first be evaluated in person for spatial potential. Ideally, the lid will be capable of holding a
⅛” thermocouple fitting and two ⅜” swagelok fittings for the inlet and outlet streams. The
lids thickness is extremely significant in this sense because it will determine what type of
swagelok fitting that can be welded in while leaving all threads easily accessible for
additional components.
7
8. The next issue is the depth of the pressure cooker’s interior. The length of the
canister and the Santoprene tubing are heavily reliant on this factor. Ideally, the interior
can support a full 6 meters of tubing with a ⅜” outer diameter, ¼” inner diameter with
enough space to easy fit and maneuver the tubing. If this is impossible, the length of the
tubing will be reduced to a functional length. Once a comfortable tubing length is
determined, the canister length will be determined. The canister length can be quite close
to the pressure cooker depth since its inlet will connect directly to the cooker lid, via
swagelok fitting, and its outlet will be an elbow coming out of the side wall and turning up
toward the lid, where the Santoprene tubing will be connected via compression fitting. The
tubing will then spiral around the canister and connect to the bottom of the double
threaded pipe leading the to the outlet of the pressure cooker.
Connecting a line of gas to the pressure cooker can can go several different ways.
Since the purpose of this cooker is to measure tar quantity, it is very important that tar
does not fall out of the gas before reaching the cooker. Thus a line coming from the gasifier
would have to either be heated or extremely short. Ideally, the pressure cooker will be
maneuverable enough to install it immediately adjacent to the sampling point so that the
line between gasifier and the cooker is a matter of inches.
This brings us to the issue of nozzle size. Gas going through the pressure system
should never exceed a flow rate of 33 liter per minute, thus the ideal nozzle size has been
calculated to extract gas from the gasifier in the above section.
After drawing gas from the gasifier and running it through the pressure cooker, it
will go through a series of other apparati. Firstly, it will run through a cool water impinger
for the purpose of removing leftover hydrocarbons. This will consist of an impinger filled
with water, set in an ice bath. After this point, the gas shouldbe clean enough to run
through a vacuum pump (to create flow), then a rotameter (to control flow), then a dry gas
meter (to measure volume), then connected to the lab’s exhaust system.
8
9. Since this is only the experimental phase, we are uncertain if the gas will be
completely clean of tars by the time it leaves the cooled impinger. To test the method, the
pressure cooker system will be connected directly to the gasifier after the scrubber, then
connected to Lisa’s tar measurement system. If the pressure cooker system works
correctly, there should be no tar showing up in Lisa’s measurement system and the cooker
and cool impinger can be connected to the additional apparati. If there isa significant
amount of tar present, the pressure cooker system will need further adjustment to remove
the rest of the tar from the gas. Such adjustment is dependent on the particular problems
that may arise.
9
