Samplingand analysis of synthetic fuel processes Obtaining meaninaful results is not a routine procedure and cannot be approached casually. It requires a professional staff capable of making in-field decisions to adjust to process changes and unanticipated problems
P. S. Dzierlenga F. G. Mesich R. A. Magee Radian Corp. McLean, Va. 221 02 Synthetic fuels based on coal gasification and liquefaction technology are prime candidates for providing environmentally acceptable uses of coal. Designing and demonstrating the technology, however, does require a complete understanding of the nature of process and emission streams in the context of available environmental control technology. For this emerging industry, this presents both opportunities and problems. Since few commercial plants are in existence, the correction of historical environmental errors is not required. The existence of pilot and small-scale units presents the opportunity to build in environmental factors at the development stage while scaling environmental data from a small unit to a commercial plant. There are many approaches to acquiring environmental data depending on the end use of the information. The EPA uses a staged approach aimed particularly at emissions. Alternate approaches concentrate on the process streams to provide data for design of treatment processes. The needs of the toxicologist are different from the design engineers. This feature relates the approach that Radian Corporation uses to design test plans for any specific end use. Radian Corporation has performed a number of environmental sampling projects on synthetic fuel processes and 288
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00 13-936X/79/09 13-0288$0 1.OO/O @ 1979 American Chemical Society
has written sampling guideline documents for both the Environmental Protection Agency and Department of Energy. Sampling projects have included the sampling of the CO2 Acceptor Pilot Plant: the Hanna In-Situ Gasification Project; and Lurgi, Wellman-Galusha, Chapman (Wilputte) and Foster Wheeler/Stoic gasifiers and attendant environmental controls. All experience to date has shown that sampling a synthetic fuel process and obtaining meaningful results is not a routine procedure and cannot be approached casually. Radian experience has been that the major requirements for a successful sampling effort are: careful planning prior to the test effort, including the development of a good sampling plan, and the use of an experienced, professional staff capable of efficiently executing the test plan and making infield decisions to adjust to process changes and unanticipated problems. Planning prior to the test effort involves determining the scope of the proposed sampling effort, analyzing the process to be sampled, selecting sampling and analytical procedures, and designating the program data evaluation requirements. This planning culminates with the development of a test plan for the environmental sampling effort.
Project scope An environmental sampling program may be initiated to achieve all or part of the following objectives: to define plant effluents to verify process compliance with environmental regulations to verify control technology performance to characterize the process or a segment of the process. Project complexity varies with program objectives. The first step in determining project scope is to define the objectives of the specific sampling effort. With the objectives established, a preliminary estimate is made of the requirements to achieve program goals, plant streams to be sampled, parameters to be measured, sets of plant conditions to be analyzed, and manpower and equipment requirements. These requirements are then reconciled with program time and budget constraints. Since there are inevitable trade-offs that occur between program goals and budget, it is recommended that a staff statistician be a part of the project team. A good experimental design should maximize the useful information resulting from any sampling effort and enhance the overall cost effec-
tiveness of the program. This input during the period when project goals are reassessed is very helpful.
Next A process analysis defines the process segments (equipment and unit operations) of interest to the characterization effort. This analysis identifies the streams to sample, components of interest, process conditions at which tests will be conducted, process data routinely monitored, and process data which must be obtained in conjunction with the environmental sampling. This step should include the performance of heat and mass balances for each process segment of interest, a tabulation of available physical and chemical data on effluent and process streams, and a determination of the residence times of the major process vessels. An important part of the process analysis is an on-site survey, which should be conducted by members of the sampling team in conjunction with the plant operating supervisor(s). The purpose of the survey is to relate the objectives of the environmental test effort to the actual equipment in the field. Such a survey provides the test crew with a better working understanding of the process and serves to minimize the number of ‘‘surprises” that may occur once the crew and equipment begin the environmental testing .
Sampling a synthetic fuel process is complicated by these factors: The physical and chemical characteristics of synthetic fuel streams pose difficult sampling problems. [Gas streams are often a t high temperatures and high pressure, and contain particulates, tars and oils. Liquid sampling may be complicated by the presence of two phases, solids in the liquid stream, or dissolved gases under pressure. Solids may be stratified making representative sampling difficult.] T h e processes are being developed and many opportunities for mechanical malfunction and process upset exist, and d o occur. It is often required to collect data from a pilot-plant or smallscale operation for application to a large-size design. In such cases, extra care must be taken in test plant design to allow correlation and scale-up of the pilot-plant data.
During this survey, particular attention should be paid to: location and physical layout of the process(es) types of vessels and equipment types and location of piping location and origin of input streams location and destination of product, by-product, effluent streams and emissions types and location of process instrumentation location and availability of sampling points. Sampling and analytical procedures are based on program objectives (scope) and results of the process analysis and on-site survey. The basic sample-selection problem is determining how best to obtain a small fraction of material that is statistically
Steps in the development of the test plan include: Definition of a process stream-analytical parameter matrix for each set of operating conditions a t which samples will be taken. Table 2 illustrates a process stream-analytical parameter matrix for sampling points and analytical parameters for the C02 Acceptor gas streams. Definition of process operating parameters to be monitored prior to and during execution of the test plant. Key process operating parameters should be monitored prior to test plan execution to establish a baseline for determining steady state conditions and to ensure that no prior process upset will influence test results. Identification of stream-analytical parameter combinations for which data from other sources (plant records and operating personnel) will be adequate. Designation of sampling and analytical techniques. Determination of sampling frequency and timing based on sampling method and data evaluation requirements. Designation of a quality control procedures for the sampling test plan. Preparation of a test schedule based on the plant operating schedule and the sampling and analysis manpower/equipment rcquirements.
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representative of the process stream. Of particular importance are the spatial and temporal variations in stream composition and the potential for changes in composition after removal from the stream. Factors which are taken into account in defining these techniques are summarized in Table 1.
Standard sampling procedures are available and are in common use for criteria or regulated pollutants in atmospheric or near-atmospheric pressure streams. Other sampling requires the adaptation or development of specialized equipment to meet the requirements of a particular process or
condition. N o two plants are likely to offer identical problems. Byapplying sound judgment, adequate procedures can be specified in the test plan.
Data evaluation and quality control The primary data-evaluation requirements to be identified for sample plan development are the number of samples or tests required to maintain statistical validity. Based on project objectives, time, and budget, an experimental design for the sampling program may be defined. Internal quality control checks (routine and random) to be made during the data evaluation procedure can also be defined a t this time (Table 2). Other quality control items established prior to sampling and incorporated in the test plan include: calibration of designated sampling and analytical equipment designation of replication during sampling and analysis identification of alternate sampling and analytical methods establishment of standard laboratory quality control procedures establishment of a chain of responsibility for data generation from sample collection to evaluation of results. Cas sampling Sampling of gases is complicated by high temperatures, high pressures; and tars, oils and condensibles. An example of this type of stream is hot product gas (1 000-2200 O F ) containing high concentrations of entrained particulates, tars and oils. Table 3 shows the gaseous organic components in the unquenched product gas from the COz Acceptor pilot plant. T o obtain a representative gas sample from a “hot” stream having high levels of entrained particulates, tars, and oils, a sample pretreatment train must be used. This train should remove the particulates, tars, and oils in a manner such that the concentrations of the gaseous species are not changed. Such a pretreatment train
should typically consist of an in-line filter, a knock-out pot, an inert filter, a permeation drier, a pump, and a flow meter. Bags or sample bombs can then be used to collect the gases for analysis. Particular problems with gas sampling are as follows: High temperatures of gas streams may require special construction materials or water, air, or oil-cooled probes. Materials of construction for sample transport tubes are shown in Table 4. High temperatures also mean that drastic changes in temperatures are required for sample handling so reactive species may be quenched. Temperature of particulate collection defines the split between particulates and condensibles so temperature must be carefully chosen if results are to be meaningful. As an example, the EPA Method 5 sampling train collects entrained particulates with the passage of the gas from the probe to a filter mounted in an oven maintained at 225 OF. This specification of a collection temperature effectively defines what material is considered to be particulate matter (materials which condense above 225 O F ) . If the primary test objective is determining the actual stream particulate content rather than verifying regulatory requirements, then collection at stream conditions is recommended. One approach which inherently requires collection at stream conditions includes mounting the particulate collection device on the end of the probe extended physically into the gas stream. This has the added advantage of avoiding losses of material to the transport-tube walls. If collection outside the stream is chosen, the sample-transport tube should be designed to minimize losses. This is accomplished primarily by providing smooth flow contours that avoid protrusions or sharp directional changes in flow and by heating the transport tube to avoid condensation. Pressurized gas streams pose access problems. These streams demand a leak-tight seal. A lubricated packing
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gland similar to valve-.steam packing is the most generally applicable option. Figure 1 illustrates such an interface. The packing gland is mounted on a fully opened gate valve or ball valve of adequate internal diameter (3 inches is generally adequate) to allow insertion of the probe assembly. The valve provides closure of the
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sampling point when not in use. Pressurized streams also mean that any particulates must be collected at stream pressure to avoid losses of material during passage through a pressure-reduction step. Since some probe losses are inevitable, the material must be recovered by washing the transport tube with suitable solvent (EPA
Method 5 specifies acetone) following completion of any collection. Filtration is the most generally applicable technique for collection of particulates; however, filters may be limited in synthetic fuel application because of pluggage from condensible tars and oils, the amount of sample required, or the reaction or sorption of
gaseous components on the filter medium producing interferences in subsequent analyses. (Studies have shown that sorption of sulfur dioxide on filter media, followed by oxidation is a significant interference in determining sulfates.) Use of a small electrostatic precipitator avoids many drawbacks present in filtration collection.
Sampling of liquids The main problems in liquid sample collection result from pressurized streams with dissolved gases, twophase (organics/aqueous) liquids, and slurry or liquid-solid streams. Open tap sampling of high-pressure liquid streams containing dissolved gases will result in a loss of dissolved gases after the reduction in pressure. If samples containing dissolved gases are desired, high-pressure bomb-sampling techniques must be used. The bomb can either be evacuated before sampling or it may be filled initially with an inert gas, such as nitrogen or helium. When the latter method is used, the initial gas pressure must be known in order to calculate the dilution of gases released from the sample on depressurization. The tap sampling of liquids flowing a t subatmospheric pressure requires pump assistance to remove the sample. The tap sampling of liquid or slurry streams at high temperature (above the liquid boiling point) requires special procedures. The liquid sample must be cooled to a temperature below its boiling point before its entry into the sample container or it will flash vaporize. The sample may be cooled by passage through an air or water jacket system before collection. Again, care should be taken to thoroughly flush all parts of the system before material is retained for analysis. In most cases, the use of a cooling system will cause some loss of sample integrity. A loss of material through deposition on the cooled wall is unavoidable. In some instances, plugging of the sample line will result. These problems can be minimized if the sample is cooled just enough to handle, but not below the temperature at which sample integrity is lost. The equipment for sampling liquids at different pressures and temperatures is shown in Figure 2 . The main problem with two-phase and slurry streams is stream homogeneity. Liquid streams tend to stratify because of different viscosities and densities. Such liquid streams should be sampled a t turbulent locations to ensure a well-mixed sample. Downstream from pumps or elbows is a preferred location. It may be necessary
to have sampling valves installed a t points where none exist.
Sampling of solids The two main problems encountered in solid sampling are the collection of a representative sample and the preservation of high-temperature reactive solids. An inherent problem with solid sampling is that solids do not mix well and tend to separate according to size and density. Obtaining a representative sample is further complicated in that solid handling does not generally create points of turbulence from which samples can be obtained. Normal sample sources are process storage areas and process conveyors. Process conveyors are the preferred sources of representative solid materials, because there is less segregation according to particle size, and the material obtained is often a sample of solids actually being used in the process. Generally, the best samples from conveyors are obtained a t the point where the exiting solid material falls vertically from the conveyor. Samples from process storage piles should be obtained by boring or augering techniques. Boring involves inserting a pipe or thief into the pile from top to bottom; the sample in the pipe represents a vertical composite of the pile. This technique cannot be used, however, with wet, coarse-grained, or lump materials. The auger sampler is particularly suitable for sampling materials that are packed too tightly for pipe or thief techniques. An auger is like a large drill bit which is turned into the pile from the top. When the auger is withdrawn, the sample is packed in the helical grooves. If necessary to prevent sample spilling, it can be enclosed in a casing. High-temperature reactive solids are another problem. These solids must be isolated from air after collection to avoid reaction with moisture or oxygen. Quenching the collected solids immediately with a n inert gas stream to conditions at which the material can be handled and analyzed is recommended. Looking ahead Environmentally acceptable synthetic fuel technologies may be developed by addressing environmental factors through sampling and analysis programs over the stages of process development. Although such process characterization may be difficult the value will be significant. The acquisition of environmental data through a coordinated effort founded on thorough understanding of the process variables and end use of the
data, will result in the most cost effective approach to data collection. This approach includes making use of the common steps and principles briefly described here, whether the end result is engineering data/health effects data or permit compliance information. These common steps are: definition of project objectives process analysis selection of sampling and analytical techniques data evaluation and quality control requirements test plan development test plan execution.
Additional reading Environmental Characterization Plan Development for a Coal Conversion Demonstration Facility, Radian Corporation, 78-200-15 1-06-05, DOE Contract EX-76-C-01-2314, May 1978. Environmental Monitoring Handbook for Coal Conversion Facilities, Oak Ridge National Laboratory, ORN L-53 19, May 1978. Guidelines for Preparing Environmental Test Plans for Coal Gasification Plants, Radian Corporation, 78-200-1 43-65, EPA Contract 68-02-2147, June 16, 1978.
P. S. Dzierlenga is a senior engineer with Radian and Dicision Manager o f t h e Radian Washington Regional Of$ce. Mr. Dzierlenga has participated in a cariety of projects concerning sjsnthetic fuel processing analyses and encironmental control technology ecaluations including prociding encironniental support sercices to Department of Energy Dicision of Fossil Fuels Processing.
F. G. Mesich (I) is an assistant cicepresident with Radian and is General Manager of the Washington Regional Office. Dr. Mesich is in charge of all program management activities on Radian technical sercice contracts. R. A. Magee ( r ) is a program manager at Radian. specializing in sampling and analysis projects. Mr. Magee has had the responsibility f o r the sampling and analysis of a wide cariety of energy technologies including a number of synthetic f u e l processes. Volume 13, Number 3, March 1979
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