Air Pollution Control Innovations

Medical Waste to Energy Conversion Using Plasma Gasification Melting

Posted by Andy Bartocci on Tue, Jul 13, 2010 @ 02:57 PM

I gave recent presentations at the International Thermalplasma gasification Treatment (IT3) Conference in San Francisco, CA and the AWMA Conference in Calgary, Canada.  The paper is co-authored with Liran Dor, CTO of EER - Environmental Energy Resources Ltd.  The paper discusses an environmentally friendly way of converting medical waste to energy using EER’s Plasma Gasification Melting (PGM) and Envitech’s wet scrubbing technology. 

ABSTRACT 

A plasma gasification melting (PGM) technology has been developed to transform waste into synthesis gas and products suitable for construction materials.   The core of the technology was developed at the Kurchatov Institute in Russia and has been used for more than a decade for the treatment of low- and intermediate-level radioactive waste in Russia. It is applicable to municipal solid waste (MSW), municipal effluent sludge, industrial waste and medical waste.

 

Plans are currently underway to build a plant in the US to recycle medical waste using the PGM technology into a high calorific Syngas and a benign residue.  Both output materials may be considered secondary materials since they have commercial use in other processes.  Current plans include the production of steam which will be sold as a commodity to nearby industrial users. 

The Syngas is fed into a Heat Recovery Steam Generator (HRSG) to produce superheated steam for use as heat or electricity generation using a steam generator. The Syngas leaving the HRSG will enter an Air Pollution control (APC) system for post process gas cleaning.  The APC system will use a wet scrubber system that has successfully achieved low emission standards on other typical combustion processes.  This paper will discuss how these technologies are combined to create an economically viable and environmentally friendly solution for converting medical waste into energy.

Please click on the below icon to download the AWMA and IT3 conference white paper. 

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Topics: gasification, biomass, syngas, tar removal

Gasification Scrubbers for Particulate Control

Posted by Andy Bartocci on Tue, Aug 25, 2009 @ 04:10 PM

Back in July I wrote a blog post for gasification syngas cleaning where I discussed two general approaches, 1) thermal tar destruction, and 2) tar removal scrubbers.  Both approaches require particulate removal. This blog post discusses several design considerations related to particulate control for syngas wet scrubber systems, including:

  1. Performance
  2. Capital Cost
  3. Operating Cost
  4. Safety

These considerations will be discussed in the context of two wet scrubber approaches for particulate control:

  1. Wet Electrostatic Precipitator

Syngas Scrubber

 Performance - The distinguishing feature between a Venturi scrubberand a wet electrostatic precipitator (WESP) is the removal efficiency for sub-micron particulate.  This is shown in the above figure which compares the particle removal efficiency for a wet electrostatic precipitator (WESP) and a 50 inch water column (W.C.) pressure drop Venturi scrubber.   The figure illustrates that both the WESP and Venturi are highly efficient for removing particles greater than 1 micron.  The removal efficiency of a Venturi, however, begins to degrade for particles smaller than 1 micron.  The Venturi performance can be enhanced by sub-cooling the gas and taking advantage of condensation effects to grow the size of the particulate.  The effects of sub-cooling to improve Venturi performance is discussed in greater detail in the Envitech paper, "Wet Scrubbing Technology for controlling biomass gasification emissions" presented at the 2008 Joint Conference: International Thermal Treatment Technologies (IT3) & Hazardous Waste Combustors (HWC)

In general, WESP's are used in applications where the sub-micron particulate concentration exceeds the capability of a Venturi to meet the performance requirements. It is therefore important to understand the following:

A Venturi scrubber will give syngas cleaning performance similar to a WESP. The removal efficiency for particles greater than 1 um diameter will be equal to or greater than a WESP.  For particles smaller than 1 um diameter, a Venturi scrubber will be less efficient that a WESP.  However, many ICE engines will most likely tolerate these particles.  Understanding the tolerance of the engine is therefore a key aspect of deciding which approach is best suited for your application.

Capital Cost - It is broadly understood that a Venturi scrubber is much lower capital cost than a wet electrostatic precipitator.  Under most process conditions this cost difference can be as much as 3 to 4 times.  The trade-off for a lower capital cost Venturi scrubber is higher operating cost to provide the pressure drop. 

The Venturi scrubber capital cost is determined predominately by the size of the gas flow.  The WESP capital cost, however, is determined by both the size of the gas flow and the desired removal efficiency.  The desired removal efficiency can dramatically affect the size and cost of the system. The higher the removal efficiency, the higher the collection area, and consequently, the greater the number of collection tubes required.   The cost of a WESP is approximately exponentially related to the required removal efficiency.  It is important to define the performance requirements before budgeting for a WESP.

In addition to metal fabrication, there are other items contributing to the higher capital cost of a WESP, including the T/R set to provide a high voltage, electronics for a more sophisticated control system, and safety interlock system.

Operating Cost - Although a wet electrostatic precipitator is higher capital than a Venturi scrubber, part of that cost is offset by lower operating cost. The pressure drop of a WESP is in the range of a couple of inches W.C. compared to 30 to 50 inches W.C. for a Venturi scrubber.  The electricity cost for the fan horse power requirements is therefore considerably lower for a WESP than for a Venturi.  There are other WESP operating costs that need to be accounted for including the electricity for the T/R sets and for the heater and blowers for the insulator compartments.

Safety - The last design consideration discussed here for a syngas cleaning system is safety.  A key aspect for a syngas cleaning system is that it contains a combustible gas.  This carries a greater risk of fire than for other types of scrubber system.  If the system is located in a confined space, it is often required for instrumentation and motors to meet division I, class II (explosion proof) requirements.  A WESP can operate in sparking mode which can be an ignition source for the gas.  Care must be taken to ensure the WESP operates in a safe condition at all times.  A WESP has additional safety interlock requirements because it operates at a high voltage.  For these reasons, a WESP it is more costly to ensure safety in a WESP than a Venturi scrubber.

Summary

  • A Venturi scrubber is lower capital cost than a WESP and in most cases is preferred if it can meet the performance requirements.
  • A WESP is generally used in cases where the concentration of sub-micron particulate exceeds the capability of a Venturi scrubber to meet the peformance limits.
  • Although a higher capital cost, a WESP has the advantage of lower operating cost. It will also achieve greater overall removal efficiency because it is more efficient for particles smaller than 1 micron.
  • Because syngas is a combustible gas, there are safety considerations for both a Venturi scrubber and a WESP. Because a WESP uses a high voltage and can act as an ignition source, the cost to mitigate safety risks is generally considered to be higher than for a WESP.

 To learn more, please download our presentation on tar removal.

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Topics: particulate control, gasification, biomass, syngas, tar removal

Ammonia in Syngas

Posted by Andy Olds on Fri, Aug 14, 2009 @ 09:00 AM

Ammonia SyngasThe primary products of synthetic gas (syngas) production from biomass are hydrogen gas, carbon monoxide, and methane.  Unfortunately, those are not the only compounds formed.  Other compounds form depending on the elemental chemistry of the biomass.  One of the more common byproducts is ammonia, released from organically-bound nitrogen.

Why ammonia rather than NOx

Organically-bound nitrogen converts to ammonia, rather than NOx, in a gasifier.   Gasifiers are typically oxygen-starved environments.  Conversion of organic nitrogen to NOx requires oxygen.  Without oxygen, combustion thermodynamics favor the production ammonia.  In fact, ultra-rich combustion environments produce reduced compounds, like ammonia, rather than oxidized compounds.

Why it is still NOx

The main goal in the production of syngas is to eventually burn it!  Ammonia left in the syngas WILL convert to NOx in a rich combustion environment, like an internal combustion engine or a syngas-fired boiler.  NOx is a heavily controlled environmental pollutant and it is important to minimize its production.

How do I remove it

Fortunately, ammonia is significantly easier to remove than NOx.  Ammonia can be removed with an ammonia scrubber using water and sulfuric acid.  Ammonia reacts with the sulfuric acid to form ammonium sulfate.  Provided any particulate is removed upstream, an ammonia scrubber can produce a very high concentration of liquid ammonium sulfate that has commercial value as a fertilizer.  Since sulfuric acid is relatively cheap, the operating costs of an ammonia scrubber are minimal. 

Ammonia gas can also be formed using a scrubber/stripper approach, first removing the ammonia in an ammonia scrubber, and then liberating the ammonia as a gas in an ammonia stripper.

Envitech's experience with ammonia scrubbing spreads into other industries.  Please read our white paper on the reduction of ammonia emissions for a sludge dryer.

White Paper

Photo Credit: ajturner

Topics: Scrubbers, biomass, syngas

Algal Gasification Treatment

Posted by Andy Olds on Thu, Aug 06, 2009 @ 09:00 AM

Last week I discussed a recent presentation on biofuels focusing on algal biodiesel.  Algae is a big topic in the biomass industry at the moment, as it offers high growth rates as compared to other forms of biomass.  The problem is that, as a new technology receiving a high level of interest only in the past 3-5 years, the optimum method for cultivating the biomass has yet to be determined.  A recent article in Biomass Magazine looks at an alternative to biodiesel: catalyzed gasification.

What does it produce?

The technology, developed by the Pacific Northwest National Laboratory (PNNL), involves the catalytic conversion of aquatic biomass.  The authors state that the process transforms the algae into methane, carbon dioxide, ammonia, and water.  Methane, of course, is the chief component in natural gas, and the main product of the process.  The authors suggest that the water and carbon dioxide can be pumped back to the growth ponds as feed.  Ammonia and sulfur products come out in the water, and must be removed prior to reinjection.  Using a train of an ammonia stripper and an ammonia scrubber, the ammonia can be converted into ammonium sulfate; possibly using the sulfur byproducts.  So far, so good.

Is it efficient?

The real interesting part of the technology is its ability to create natural gas from the aquatic biomass without drying the biomass, which represents a huge drain on the thermal efficiency.  The article suggests temperatures of 350C (662F), but under pressure, so the water remains a liquid.  If true, rather than expending ~1115 BTU/lb to dry (evaporate) the water from the biomass, the process only uses ~670 BTU/lb to heat the water, a thermal savings of 40%.

Too good to be true?

I do have some reservations about the technology as presented.  The biggest drain on biomass is the amount of water contained in the biomass.  Water is an energy sink - it does not combust and reduces the combustion of heat of the biomass.  Any savings offered by this process is dependent on the ability to generate a "dry" biomass.  I typically see biomass sources containing 20% biomass and 80% water.  An algae stream with 10% biomass would have twice as much water, and would lose the gain in thermal efficiency as it has to heat twice as much water.  The math only works if the biomass is concentrated. 

And that may be only half the problem.  My experience with fluidized beds is that there is a limit to the concentration of solids in a fluidized bed.  The simplest way around that is to recycle the water produced in the process (which presumably is still hot and pressurized).  However, that is still a loss in the system, and the exact solids concentration limit will have an impact on the efficiency of the process.

Final thoughts

I believe, as stated in this article, that harvesting algal biomass is quite possibly the most critical step to its economic viability.  Water is an energy drain on all of biomass.  PNLL and Genifuel look to have found one way to possibly reduce the cost.  Further, I like their approach at looking at waste streams first, as solving a wastewater discharge problem improves the economics of the process; it is one of the reasons that waste to energy projects have succeeded.

To read more about ethanol recovery, please download our presentation at the 2009 FEW conference.

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Topics: gasification, biomass, syngas

Biofuels Presentation II

Posted by Andy Olds on Mon, Aug 03, 2009 @ 09:00 AM

On Wednesday I discussed the first part of Professor Steven Briggs presentation on biofuels.  The second part of Professor Briggs presentation was specific to algal biodiesel.  Like Wednesday, I will provide a bit of commentary on some of his remarks (underlined, paraphrased).

algal biomassBiomass Production

  • Algal - 48 metric ton/acre/year
  • Switchgrass - 12 metric ton/acre/year
  • Sugarcane - 10 metric ton/acre/year
  • Corn - 6 metric ton/acre/year

The information above was one of several slides that Professor Briggs used to make a point on the effieciency of algae in converting to biomass.  I believe Briggs was indirectly tackling the land use issue.  For those a bit removed from the biomass industry, there is a growing land use issue that both Andy B and I have heard about at recent ethanol conferences.  The theory is that land use for energy will replace acreage that is currently absorbing carbon dioxide (by way of trees and foliage), converting the land from a carbon sink to carbon neutral, and thus increasing the amount of global warming.  It is an interesting and complex topic, and given Briggs attention to land use in his presentation, I believe it is likely to be used as a counterargument to biomass collectively, whether it is true or not.  In any event, it is becoming important politically to maximize yield per acre, as there are other thorns on the land use issue (food production, fertilizer run off, genetically-modified plants) even if this one is resolved favorably for biomass.

biodiesel fuel

 

 

We need to refine biodiesel to higher grade fuels 

Professor Briggs presented a wonderfully simple flow chart showing the steps from farming to fuel.  There were several steps in the process where Professor Briggs noted that algal biodiesel was not yet efficient enough for commercial production, but the most interesting step for me was the refining process.  Refining biodiesel is essentially maximizing the production of low molecular weight carbons and increasing the heat content of the fuel.  However, there is also a third goal of refining, and that is in minimizing the production of secondary pollutants (sulfur oxides, nitrogen oxides, and chlorides).  A great deal of time and money has been spent to minimize the secondary pollutants produced by hydrocarbons.  Will biofuels be able to capitalize on these technologies, or will there need to be new technologies developed to reduce secondary pollutants?

One final note - Professor Briggs displayed a colorful table at the end of his presentation showing a variety of fuel sources in rows (hydrocarbons, algal biodiesel, electricity, etc.), a variety of issues with those fuels in columns (cost, security, availability, etc.) and a green (good), yellow (fair), or red (bad) symbol in each box for their impact.  Teasingly simple, it also suggested that there is quite a fight amongst "green" energies - all of algal biodiesel boxes were green, while other green sources were noticeably multi-hued - despite the lack of an in-place commercial-scale techology (isn't that a bit important?).  I guess competition in the green industry is no longer just limited to beating up hydrocarbons.

For a presentation on ethanol scrubbing, download the presentation below.

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 Photo credit: higetiger, octal

Topics: ethanol, biomass, syngas

Biomass Presentation I

Posted by Andy Olds on Wed, Jul 29, 2009 @ 06:34 PM

biodiesel fuelYesterday I attended a presentation on biofuels by Steven Briggs, a biology professor at University of California, San Diego.  Professor Briggs possesses a wealth of academic and industrial experience with genomics and biofuels, including corn ethanol, biodiesel, and algal biodiesel.  Undoubtedly, Professor Briggs is an expert in bioenergy, and the overwhelming attendance indicated the importance of the industry to the greater San Diego area.  Today I would like to highlight some of the topics Briggs spoke on (underlined, paraphrased).

Liquid hydrocarbon fuels account for 41% of the energy consumed

Professor Briggs highlighted the tremendous consumption of liquid fuels, primarily oil.  Briggs later noted that there is an existing infrastructure for liquid fuels. 

What does this mean?  Biofuels that are compatible with existing hydrocarbon infrastructure have a tremendous financial advantage.  All of the biomass projects I have seen create energy or fuel that fits into existing infrastructure.  Ethanol, for instance, has found a market as a replacement for liquid hydrocarbons precisely because it can be used within the existing infrastructure (car engines).  As Professor Briggs noted though, ethanol is more corrosive than oil, which has prevented its use in the existing infrastructure that transports oil from refineries to gas stations.  Other projects I have seen include converting wastes (biomass) into electrical or steam energy, or into solid fuels for use in cement kilns.  The common thread for current projects: Apply renewable fuel sources to existing infrastructure.

Oil production in the United States peaked in 1970.  Using theories derived from oil production in the United States, and that of coal production in England, worldwide production of oil is expected to have peaked in 2005.  Early estimates indicate that this may be the case.

Has the world hit the downslope of oil production?  There are far-ranging impacts to a decrease in oil production, both economic and political.  For the biofuels market in particular, it may lead to higher prices for hydrocarbon fuels and more cost-competitiveness, one of, if not the key obstacle that biofuels must overcome.  A further sign of a drop in oil production might be in the flurry of activity in biofuel research by traditional hydrocarbon-based companies.  Exxon-Mobil, Chevron, and British Petroleum have all made recent announcements of significant investment in biofuels.

The United States has set a target of 24% of all energy consumption from renewable fuels by 2022.

Briggs provided a table with mandates for renewable energy consumption for a number of countries.  Briggs was quick to point out that the mix of renewable fuels to meet this target is yet to be determined.  Obviously though, consumption will be driven to the lowest cost fuel that meets the definition of renewable fuels.  Hydrocarbon liquids have such a huge share of the energy market because they are precisely the lowest cost fuel.  We can reasonably expect that the lowest cost renewable energy fuel will corner the market in the same fashion that hydrocarbons have for the past 200 years.

I will have more on the second part of Professor's Briggs presentation, algal biodiesel, in my next post.

For a presentation on ethanol scrubbing, download the presentation below.

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Photo Credit: Binary Ape

Topics: ethanol, biomass