Solids

The best way for chemical processes to deal with solids is to turn them into liquids.  This is not always possible, so solids materials handling must consider important factors for success.  Solids will hang up, plug and rat hole.  Solids will segregate.  Solids have the unique property that they can de-mix if they are over mixed.  Solid particles will break down and they will also agglomerate.  Attrition of engineered particles contributes to increased pressure drop in systems where they are used as catalysts and sorbents.  Product delivery to consumers can be affected by over dusting due to the breakdown of the particle structure.  When suspending solids in slurries for liquid phase transport, solid particles will settle in and plug slurry lines.  Dust will have to be controlled.  The small particle emissions from systems have been identified with many repository aliments and have become a focus area for control.

For more on solids:
Solids Characterization

Slurries

Pumping slurries and keeping slurries agitated in tanks are two of the most difficult transport operations in chemical engineering.  Provisions must be made in the design to keep all slurries moving so as to not have them plug lines or plug the bottoms of agitated tanks.

Many times engineers designing system do not take into consideration all the transient and failure modes that may effect the slurry handling systems design.  For example, slurry tanks should have provisions to allow the re-start of the agitator in a tank bottom where the solids have settled into a cake in around the impeller.  System design methods could include high torque agitator drives, shafts and couplings, back up electrical power, or decoupling and mechanical torque multipliers to assist in the restart.  Methods to get the slurry moving in the bottom of a settled tank could include installing access for air lances to be placed into the caked up tank to begin to move the material using air then allowing the agitator start up to finish the re-suspension of material. 

To insure that the production of the needed sales specification material is achieved 100% of the time, a Statistical Process Control methodology will be used to determine the needed production targets.

For more on slurries:

Statistical Process Control

Statistical Process Control is a method of trending and analyzing both on line continuous and off line discretely sampled data for a process.  Metrics are established determining the performance of the system considering the variability that is inherent in the system.  The information presented for decision-making is delivered with the known errors so that the quality of the data can be appropriately applied to the nature of the decision being made on that data.  A common goal is to have all production specifications achieve and maintain a cpk of 1.33.  All measured control variables should only be reported from validated test methods or field instruments by qualified operators and analysts. 

All measured control variables shall be refereed by a laboratory that has greater validated precision than the plant claim and has accuracy tied to an NIST standard.  The referee validation of the plants measurements for each measured variable shall occur at a frequency no less than once per year.  No unit should be permitted to pass on a quality problem downstream for others to fix. 

The Western Electric Run Rules should be applied to each units measured control variables so that corrective action is taken prior to the control variable going out of specification, however action is not taken in response to the natural variability in the system.

For more on Statistical Process Control:
Statistical Process Control and Statistical Quality Control

Brines & Wastewater

Brine streams are prevalent in many industries.  Mining, waste water treatment, and desalinization systems all have brine treatment components to them.  A newer brine stream becoming very important is the treatment of production water.  Production water is a product of natural gas and natural gas liquids recovery operations.  It is primarily derived of flow back water from the well operations.  The recovery, processing and reuse of production water is becoming increasingly the key to unlocking the potential of the California natural gas resources in both the Monterey and Santa Maria plays.  Without the ability to process the volumes of production water, the use of water for the natural gas recovery operation becomes limited.  The natural gas and the natural gas liquids that can be brought to market using the emerging drilling and recovery methods represents a significant long term opportunity for the California economy.

For more on water recovery:
Water Recovery from Brines and Wastewater

Chlor-Alkali Systems

A chlor-alkali plant is a specialized type of chemical plant operations.  Using DC power, electrochemical cells split an ultrapure sodium chloride brine into its constituent components, chlorine, hydrogen and sodium hydroxide.
The plant can be separated into the following units:

  1. Brine
  2. Cell and Renewal
  3. HCl Burner
  4. Caustic Evaporator
  5. Bleach
  6. Utilities

The critical factor for any chlor-alkali plant is the purity of the brine fed to the cells.  The ability to remove low level constituents from the brine is the key to any chlor alkali operation.  

For more on Chlor-Alkali systems:
Chlor-Alkali

Foods Processing

Foods processing utilizes similar process development techniques in scale up and manufacturing as other process development efforts.  What sets foods processing apart from a typical non food and drug consumer packaged good item is adherence to the specific regulatory guidelines including the cleaning, sanitizing, and sterilization of processing equipment on a regular basis.  

Cleaning must be done thoroughly to fully remove any locations that can harbor active organisms under hard scale or in multiple unaffected and layers of soil insulated from the cleaning method. Cleaning usually has two common methods: Clean In Place, known as CIP, and Clean Out of Place or COP.

Sanitizing is the deactivating of any residual exposed organisms left on surfaces after cleaning. Sanitization is not effective without being preceded by an effective cleaning. Sanitization is completed by using heat and or chemicals to kill a significant percentage of any organisms and render the surfaces under control from contamination by reducing the colonies of organisms. 

Sterilizing surfaces requires the removal and kill of all contaminants on the surface. Usually sterilization is a heat step following a cleaning and sanitization.

             For more on Foods Processing systems:
             Cleaning, Sanitizing and Sterilizing
             Typical Cleaning and Sanitizing Solutions
             Sampling and Analytical Technique Considerations for Microbial Surface Swab Testing

Lithium Extraction

Lithium extraction from brine is a promising new source to supply the growing lithium market.  Demand is growing with the emergence of the lithium battery powered automobile.  Battery development is generating many improvements in the energy storage capacity, however most technology has lithium as a key component to the system.  The demand for lithium should continue to rise as the popularity of the battery powered car grows.  A typical lithium plant can be broken down into the following six major unit operations, each a plant onto themselves.

  1. Ore Extraction
  2. Brine Preparation
  3. Lithium Extraction
  4. Purification
  5. Product Conversion
  6. Utilities

The critical factor for the lithium extraction plant is control of the separation effectiveness of the constituent removal unit operations.  Batteries require high purity lithium.  The ability to remove low level constituents from the product is the key to any lithium operation.  

Rare Earth Processing

Rare earths are extracted from bastnasite ore using many common hydrometallurgical methods designed for the particular application.    Demand for rare earths has been variable due to the dominant positions of producers in the market.  A typical rare earths operations can be broken down into the following major unit operations, each a plant onto themselves.

  1. Mining
  2. Milling
  3. Tails
  4. Separation
  5. Concentration
  6. Purification
  7. Product Conversion
  8. Utilities

The critical factor for the rare earths plant is control of the separation effectiveness.  As with all combined mining and chemical operations, the efficient use of energy and water is also critical to the success of the plant.  The detail is a fascinating and exciting chemical engineering endeavor.

Gas to Liquid

The fracking boom has increased the amount of natural gas available on the market.  To sustain the economic viability of continued production, new market outlets are continually being developed.  The previously interesting biogas market has been hurt by the flood of lower priced natural gas available.  One market that has not yet drawn sufficient need on the natural gas market is the liquid fuels market in using the available natural gas as a feedstock.  A wide variety of waste material can be collected and used for conversion to fuel feedstock using a consortium of bacteria if the product market had margins to support the systems.  A process system that could be added to the biogas systems are conversion systems to produce liquid transportation fuels from the biogas.  Liquid transportation fuels represent one of the largest market outlets for energy.  A biogas to diesel conversion system design is needed to drive environmental and market positions.

Biodiesel Production

Biodiesel is made by reacting a triglyceride with an alcohol traditionally in the presence of a base catalyst, and most recently without catalyst using supercritical fluid process conditions.  The reaction is known in general terms as transesterification.  The resulting desired product is a fatty acid methyl ester (FAME) when using methanol as the reacting alcohol.  The FAME is the biodiesel.  Acid catalysts can also be used, but the transesterification reaction is much slower.  The supercritical system has also been successful in creating fatty acid ethyl ester using ethanol as the reacting alcohol.  Traditionally, base catalyzed biodiesel systems need low free fatty acid feedstock to avoid the formation of soap.   The supercritical system uses various levels of free fatty acid feedstock as the competing soap reaction is not a factor.  Other methods of converting high free fatty acid feedstocks have been successful by first esterifying all the FFA then transesterifying the remaining triglycerides in the feedstock.    The two key process chemistry concerns is the moisture in the reaction system and the level of free fatty acid in the feedstock.  The published water effect on these reactions is conflicting at the moment, but it has been found that if water in excess of 5 wt% is allowed to build in the reactors, then the reverse reaction will overtake the desired fatty acid methyl ester reaction and the conversion of the feedstock will become severely affected.  Since water is a factor in the alcohol separation as well, and water is created in the conversion of the free fatty acid in the feedstocks, the amount of water in each stream must be managed carefully to insure that the conversion is not affected beyond economic practicality.  In these systems, feedstock moisture was managed below 0.5 wt%, and the separation of the FFA reaction created water from the methanol stream was controlled to no more than 2 wt% in the recycled methanol to control the buildup of moisture in the downstream processes. 

Biodiesel production systems technology application is dependent upon the feedstock available for conversion.   Cold pressed seed oil systems are simple and can be operated at reasonable temperatures and make use of more straightforward extraction washing systems.  As the feedstock becomes lower quality as defined by higher free fatty acid and increased moisture, the unit operations needed for conversion become more complex. Usually as feedstock FFA is higher so is the sulfur.  Sulfur is usually not a problem in cold pressd seed oil feedstocks, but it becomes a significant factor in the use of brown grease and especially in the use of waste oil feedstocks.  Considerations must be made as to feedstock issues and reaction preparation, analytical methods, conversion efficiencies and finishing system effectiveness.

Feedstock Characterization:

Traditional Batch Base Transesterification
- Feedstock less than 1.0 wt% FFA, and 0.5 wt% water.
Continuous Using Intensification
- Feedstock less than 4.0 wt% FFA and 0.5 wt% water.
Supercritical
- Feedstock up to 90% FFA and less than 1.0 wt% water.
 
Key Biodiesel Considerations:
 - Water affects all reactions.
 - Less catalyst is required when using intensification.
 - Supercritical conversion is higher with higher FFA feedstock
 - Glycerol dehydration is a concern in the supercritical reactor
 - Distillation affects analytical methods
 - Finishing systems are critical to meet ASTM 6751 specifications
 - Sulfur levels are significant in higher FFA feedstocks

Biofuel Sulfur Removal

Bio feedstock derived diesel is produced by esterification, transesterification and hydrogenation reactions and sold as either biodiesel which meets the ASTM 6751 fuel specification or as green diesel which meets the petroleum feedstock derived diesel ASTM 975 fuel specification.  Both specifications have a limit of no greater than 15 ppm sulfur be present in the fuel.  Repurposed waste bio derived feedstocks have higher levels of sulfur than the more common and higher cost virgin bio based feedstocks. 

Sulfur is present in many forms.

Large petrochemical refinery operations use hydrodesulfurization as the primary unit operation.  This has been traditionally economical at a large scale.  The 15 ppm sulfur limit in diesel fuel has presented even the long established refinery operations a challenge as with any separation as the permitted levels reduce, the amount of effort for further reductions increases.

Many of the unit operations in the process of converting feedstocks to fuel have equipment and conditions that can be modified to progressively remove sulfur in each of the steps.  Typically the repurposed waste has additional process steps to make the material suitable for the downstream unit operations.  The most useful removal steps that might be present in the current systems are the physical and chemical separations and the conversion reactions themselves.  These could include filtration, centrifugation, adsorption, and distillation.  In the case of green diesel production, the hydrogen reaction step not only produces the fuel components, but also reacts with the sulfur to allow it to be separated in downstream unit operations. 

For more on sulfur removal from biofuels:
Combinational Unit Operation Strategies for Sulfur Removal

Biofuels

Grease Trap Waste to Feedstock to Fuel

GTW to Feedstock to Fuel

Every commercial kitchen has a grease trap that allows the food waste and fats, oils and grease (FOG) from the food preparation to be separated from the water effluent that is then discharged to the sewer.  In recent years, more attention has been focused by local wastewater system operators on the problems associated with having FOG solidify in the public sewer piping causing blockage and significant overflows.

Grease Trap Waste (GTW) is the waste that is in the trap, this term includes all the water, solids, oils and grease.  Waste Trap Grease (WTG) or simply “trap grease”, usually only refers to the grease portion of the total mass in the trap.  GTW is difficult to sample, and difficult to characterize due to its variability.  Usually, it is mostly water.  The oil content can vary from as low as indistinguishable to at times be as high as half and half water/solids and oil.

Feedstock Characterization
The most important area of focus for converting waste to fuel is the feedstock.  The variability in the physical and chemical properties of the waste material requires a front end process that is able to stabilize the characteristics of the feedstock for successful conversion.  Biodiesel production can be accomplished by various methods once the oil is free of solids and moisture.  The first step is to sample and analyze the feedstock:

1. Daily samples using methods insuring uniformity and rigorous analysis aliquots
2. The critical measures are:  moisture, insoluables, solid particle size, FFA and sulfur
3. If polymers are used in dewatering, they could be a source of difficulty
4. Melt point indicates the triglyceride and free fatty acid mix.  Details require a GC-MS analysis.

Progressive Separations
The material is physically separated progressively using screens, heat and g-force devices.  Collected GTW  traditionally is dewatered using chemistry and filter boxes.  The material interception point will guide the proper feedstock processing methods.  Settling tanks can be used to minimize capital for low volume operations.  The following steps produce an oil ready as feedstock for multiple types of conversion processes.

Heat, Decant, and Centrifuge

Conversion to Fuel
Traditional base catalyzed transesterification requires low FFA feedstock.  Prepared and separated WTG is usually higher in FFA than allowed for this conversion technology.  High FFA WTG can be acid esterified followed by a base catalyzed transesterification to produce biodiesel.  These can be accomplished with either homogeneous or heterogeneous catalysts.  Removal of the water formed during the acid catalyzed reaction is the critical control element for overall success.  High FFA feedstocks have been successfully converted using the supercritical process.  The choice of conversion technology to apply goes back to the feedstock characterization.  Low percentage blending with higher quality feedsotcks has also had economic success depending upon the details of the feedstock characterizations involved. 


 

Documents for Download:

Activated Carbon

Activated carbon is used in primarily two forms: Powdered Activated Carbon (PAC) and Granulated Activated Carbon (GAC). 

PAC is crushed or ground carbon particles.  The American Water Works Association Standard (AWWA) defines PAC as any carbon finer than GAC.  GAC is retained on a 50 mesh screen, PAC will pass a 50 mesh screen.  The American Society of Testing Materials (ASTM) classifies PAC as passing an 80-mesh sieve.  PAC is added directly to other process units and filtered.  PAC will usually create too high of a pressure drop for use in packed bed columns.  GAC is commonly used in packed bed columns.

GAC can be granular or extruded.  GAC is designated by mesh sizes such as 8 by 20, 20 by 40, or 8 by 30 for liquid phase applications and 4 by 6, 4 by 8 or 4 by 10 for vapor phase applications. A 20 by 40 carbon is made of particles that will pass through a U.S. Standard Mesh Size No. 20 sieve but retain on a 40 mesh screen.  AWWA B604 specifies a 50-mesh sieve as the minimum GAC size. The most popular aqueous phase carbons are the 12 by 40 and 8 by 30 sizes as they balance of size, surface area, and pressure drop.  GAC particle size will determine the flow properties of the column.  Liquid and gas adsorption and absorption use different cuts for performance.