FGD and Heat Recovery Hot Topic Hour on June 16 reveals Unique Opportunities for Power Plants

New Structure with Free Decision Guides for Power Plants around the World

The Hot Topic Hour held on the June 16 was focused on the removal of SO₂ and SO₃ from power plant stacks but also provided lots of innovative ways to make power plants more efficient by sorbent injection and heat recovery.  More importantly it demonstrated that there are new paths for power plants to gather the key information for decision making and for suppliers to communicate with the power plants in a way where the lowest total cost of ownership can be determined for the product in question.

•      The challenge is to convince the decision maker in Vietnam that the higher efficiency blower will reduce electricity costs and more than offset the initial price or that the membrane bag will last enough longer to justify its higher price. There are three elements to success in this quest:

o   Create a clear case for the LTCO

o   Identify the decision makers

o   Convince the decision makers.

Free decision systems for power plants provide the route for vendors to make their case. McIlvaine is providing free access to recorded webinars and to certain publications for end users around the world. They are also reached with a bi-weekly Alert and 4 weekly newsletters. The supplier can best leverage this opportunity by making sure their information is displayed.

The end users have free access to the following publications:

•      44I Power Plant Air Quality Decisions (decision guides on mercury, FGD, DeNOx, precipitators, fabric filters, valves, pumps, and other subjects).

•      59D Gas Turbine and Combined Cycle Decisions (decision guides on GT intakes and GT emission control as well as many other subjects).

•      1ABC Fabric Filter (decision guides on cement, steel, waste to energy, and other subjects.

•      2ABC Scrubber/Adsorber/Biofilter Knowledge Systems (decision guides on sewage sludge, waste-to-energy, mining, and other subjects.

•      3ABC FGD and DeNOx Knowledge Systems (FGD and DeNOx decision guides).

•      4ABC Electrostatic Precipitator Knowledge Systems (coal particulate decision guide).

•      9ABC Air Pollution Monitoring and Sampling Knowledge Systems (decision guides on use of CEMs as well as water monitoring subjects.

Dry Scrubbing is extensively covered in the decision systems.

There is a subsidiary website in Power Plant Air Quality Decisions focused just on dry scrubbing. It addresses questions such as

•      How efficient is DSI?

•      Where is sodium a better choice than calcium?

•      What improvements are achieved by using special high reactivity hydrated lime?

•      How widely will DSI be used in terms of which industries and which geographies?

•      Is McIlvaine on the right track recommending an analysis of FIFO/LIFO to ensure that the first sorbent on the cake is pulsed and not the fresh unreacted sorbent?

•      For medium sulfur coals, can a combination of DSI and a spray drier be competitive with circulating dry scrubbers?

•      How much progress is being made on using DSI solid waste and converting it into bricks and building materials?

•      Should every power plant using high sulfur coal consider DSI ahead of the air heater to reduce SO₃ and to be combined with an air heater upgrade to further reduce gas temperature?

•      Can DSI with ceramic catalytic filters replace all the other APC devices?

One of the decisions is the type of dry scrubber that is best. Originally SDA was the main option. Now CDS is popular. DSI with the more reactive sorbents has become an option even when higher efficiency is required.

The catalytic filter with DSI promises one stop shopping. Combinations such as DSI and SDA are also an option. FSI + Catalytic Filtration + Condensing Heat Exchangers (CHX) - How to make Pollution Control Profitable by Martin Schroter, Dürr Systems - Hot Topic Hour March 19, 2015.

The dry scrubber is necessarily part of a multi pollutant removal system that addresses particulate, acid gases and toxic metals. As a result, evaluation of the impact of the dry scrubber on the removal of pollutants such as mercury is important. The changing regulations in the U.S., China and the EU all need to be addressed.

Solid waste is an issue. Can the sorbent/acid/ash combination be used as construction materials?  What about leaching of toxic metals?  The loss of flyash and gypsum revenues need to be evaluated. The benefits of lower water use and elimination of wastewater are also important.

There are many process factors. One is the sulfur content of the fuel versus the required efficiency. Another is the temperature of the air leaving the heat exchanger and the potential for DSI ahead of the air heater to allow greater heat recovery.

LIFO vs. FIFO for SO₂ capture 

The recent regulation of many pollutants combined with new technology, which makes it possible to remove all the pollutants in one device, has greatly increased the use of fabric filters. However, there has not been a recognition of what McIlvaine describes as “The importance of FIFO vs. LIFO in Dust Cake creation.”

Direct sorbent injection (DSI) and embedded catalyst dictate a new approach to bag cleaning.  In addition to discrete particle capture, bag filters are being tasked with: 

•      Mercury removal

•      Acid gas absorption

•      Dioxin destruction or capture

•      NO_x reduction

The importance of the method of bag cleaning can be illustrated by use of the accounting approach to inventory. Two options are first in first out (FIFO) and last in first out (LIFO). If the price paid stays the same, the choice between the two accounting methods makes no difference.  But, if the cost of recent inventory is greatly different than the past, then the accounting method makes a big impact on profits.

The capture of discrete particles is the equivalent of price parity. Let’s say that when you pulse a bag you are always discharging the latest particles to arrive and the remaining cake consists of the earliest. Since the ability of a matrix of dust particles to act as a filtration medium does not change, it does not matter which particles remain. In fact, maintaining a somewhat permanent layer of cake protects the fabric from wear. Also a more permanent cake provides higher dust capture. It has been shown that on-line cleaning results in some re-deposit of dust particles. But this is does not impact discrete particle capture efficiency.

The new paradigm with DSI is a big price difference. The newly arrived lime particle has the capability to absorb acid gases. The lime particle deposited earlier is already converted to calcium sulfate and provides no additional absorption capability. The semi-permanent cake layer is very undesirable for acid gas capture. Mercury re-emission is also a risk for an activated carbon cake which is semi-permanent. So it is very important to adopt FIFO and not LIFO.

This leads to the obvious question as to which are the best cleaning methods to achieve LIFO?  The long running debate about surface filtration vs. depth filtration needs to be reviewed in light of FIFO. Also, the pulsing method itself needs to be reviewed. Do some methods result in more re-entrainment of particles in the previous cake than do others? Should more of the cake be removed with each pulsing?

It could be argued that the reaction takes place in the ductwork and not on the bag.  But the big difference in performance of bag filters vs. precipitators with DSI proves that the cake absorption is substantial.

There may be lots of research on this subject but if so, McIlvaine would appreciate feedback on it.  If there is not, it is an area deserving lots of attention.

Bag cleaning is also made more challenging by the increasing use of ceramic filter elements. The advantage of these elements is the ability to remove dust at 850°F. The older generation rigid ceramic has been replaced by ceramic fiber media which can be pulsed. However, this media cannot necessarily be pulsed with the identical system used for synthetic bags. An alumina refinery in Australia was having cleaning problems with a ceramic filter. Pentair-Goyen analyzed the situation and provided a more robust pulsing system. This solved the problem.

Ceramic, glass and even synthetic media are incorporating catalyst in the media to reduce NO_x or oxidize dioxins. Do these designs require a different cleaning approach?  The catalyst in the Clear Edge design is not on the surface. So, the dust cake will not affect performance except if it causes maldistribution of the gas. If more gas flows through one area than another, the reactivity of the system is reduced. 

A broader subject is the whole approach to cleaning. High pressure/low volume is the most popular option. Does capture of these other pollutants open the door for high volume /medium pressure or even for reverse air cleaning? 

The potential for the one-stop shopping is great. Costs of pollution control can be reduced for new installations. The small footprint makes a big difference in the cost of upgrading existing plants to meet new air pollution rules. It is, therefore, important to understand and then maximize FIFO potential.

We asked Pentair-Goyen to provide us with the parameters which they believed would be important in fine tuning the bag cleaning to achieve FIFO. They provided a listing in four segments.

A number of participants indicated that they believe this is an important subject for investigation.  Marty Dillon pointed out that the retention of mercury on the dust cake is also an issue. Mercury re-emission is more likely to occur with LIFO. McIlvaine is looking for additional input on this subject. Pentair-Goyen indicated their willingness to participate and to optimize cleaning for dust, acid gases and mercury.

Utility participating today wants to eliminate Sodium Sulfate Ponds

A utility participating in this discussion has contacted us and asked for our recommendations on how to eliminate the sodium sulfate pond.

•      One option would be a double alkali system. Neumann says that their Colorado Springs installation has the right chemistry to eliminate excess sodium sulfate. The Colorado Springs Drake 6 & 7 use a double alkali system with sodium as the scrubbing agent. The units began successful operation in March 2016.  The question relevant to the utility wanting to eliminate the sodium ponds is whether the Colorado Springs technology can be economically applied to the existing utility scrubbing system?

•       Another option would be to switch to Thioclear. The benefits are a magnesium oxide by product as well as gypsum.

•      What about ZLD using forward osmosis?

Two-Stage Scrubbing with Rare Earth, HCl, and Gypsum Byproducts

Two-stage wet scrubbing can be utilized to produce rare earths, 30 percent hydrochloric acid and gypsum. DOE has just awarded 10 grants to pursue rare earth extraction from flyash. Previous studies have shown that rare earths can be economically extracted from a number of types of coal flyash. The processes investigated by both DOE and the Chinese government are based on digging up flyash from landfills and going through the expensive size reduction processes. Acid leaching is then employed.

The two-stage scrubbing process would eliminate much of the expense. The flyash and HCl are captured in the first scrubber while the SO₂ is captured in the second. A WESP is needed for final particulate cleanup because the dust load leaving the first scrubber will be around 0.l lbs/MMBtu.

By recycling the scrubbing liquor in the first stage and maintaining a pH of 1 by a controlled bleed stream a dirty 30 percent hydrochloric acid stream is maintained. The dirty acid is then already in a condition for leaching of the rare earths. McIlvaine was President of Environeering when it teamed with United Engineers to provide two-stage scrubbers at Philadelphia Electric.  A number of waste incineration facilities in Europe are making hydrochloric acid and recovering the metals. So the technologies are well established.

When McIlvaine initially published the information on the two-stage scrubbing approach there was immediate interest and inquiries from DOE. But subsequently nothing transpired.

Improving Plant efficiency by capturing Waste Heat will go a Long Way to meeting Future Regulations

•      Proposed U.S. standards for reducing carbon emissions from existing coal-fired power plants rely heavily upon generation-side efficiency improvements. Fuel, operations, and plant design all affect the overall efficiency of a plant, as well as its carbon emissions.
 

•      The beneficial use of more flue gas heat can substantially contribute toward meeting these goal.

•      FGD and sorbent injection can all play a role in reducing the emissions. Presently FGD increases the emissions by adding pressure drop and increasing fan energy consumption.

Benefits of combining Sorbent Injection and expansion of the Air Preheater

•      Allows lime to be used for DSI without increasing particulate emissions.

•      Increases boiler efficiency.

•      Decreases fan horsepower.

•      Can reduce precipitator emissions without DSI from 25 mg/ Nm³ down to 10 mg/ Nm³.

•      Can allow use of less expensive bags (lower temperature resistance).

•      Sorbent injection also improves NO_x capture by allowing more ammonia slip.

•      Enhances mercury capture due to eliminating SO₃ competition.

•      Eliminates SO₃ and sulfuric acid mist.

•      Lower FGD water usage.

Arvos and AECOM have teamed to combine air heater enlargement and sorbent injection to substantially increase power plant efficiency.  A 500 MW power plant in Indiana is successfully operating with sorbent injection to reduce SO₃ followed by a modified air heater and is achieving a 70 percent reduction in air preheater outlet temperature with no increased maintenance.

Gus Shearer of Arvos was optimistic about the size of the potential market for this technology. There was some discussion of the Chinese market and the need to reduce precipitator emissions. Some plants are installing WESPs but the air heater upgrade would be much more economical.  The Chinese are even more concerned about air heater performance than most countries. Whereas most operators are content with 6 percentage in-leakage to the air preheater, the Chinese are striving for only 3 percent, according to Gus.

The reduction in precipitator emissions has been well documented by Mitsubishi and Hitachi.  Close to 10,000 MW of Japanese coal-fired capacity uses heat exchangers which reduce the inlet precipitator temperature to 195°F.  At the lower temperature the precipitator that was emitting 25 mg/Nm³ of dust is now emitting 10 mg/Nm³.

Howden has the Package including Air Preheater, Fans, and Blowers (conveying Lime)

•      Howden Group has extensive international experience in the manufacture, turnkey installation and operating characteristics of heavy duty fans, rotary air preheaters and Gas Gas Heaters – with present major markets being in China and the Far East.

•      Their activities have focused on emission reduction systems by reducing the leakage levels and improving the availability and thermal efficiency of these rotary heaters.

•      Various coal-fired plants have benefitted from using Howden’s VN sealing retrofits, special element designs and on-line HP washing of the element baskets.

•      While these maximize availability and maintain plant performance over time, thereby reducing the need for DSI, such modifications are complementary to sorbent injection when targeting reduced flue gas temperatures and mercury emissions.

•      Howden’s acquisition of Roots Blowers in 2015 brings further product capability within the power sector for the pneumatic conveying of DSI.

•      End users have significantly reduced their operating cost and increased revenue by optimizing the combination of heater elements, on-line HP washing and APH sealing and draft fan upgrades.

•      Reductions in gas volume flow associated with sealing retrofits and reduction in gas outlet temperature significantly improve the performance of both ESPs and FGD plants while minimizing fan power.

•      When considering additional plant items, optimization may be constrained by the plant layout.

•      Integrated plant solutions achieve emission reductions with reduced unit heat rate and provide extended plant life.       

Anqing heats Boiler Feedwater

Shenhua Shenwan Energy Company’s Anqing Power Plant Phase II’s 2×1000-MW expansion project includes many energy saving features. An approach to saving energy was capturing the waste heat in the flue gas and using it to preheat the boiler feedwater. Operating at the designed full load, the flue gas heat exchanger recovers 44,000 kW of heat, which reduced heat consumption by 45 kJ/kWh, and reduced the plants’ standard coal consumption by 1.65 g/kWh.

Co-locating Municipal Wastewater Treatment Plants and Power Plants

Municipal sludge and treated wastewater are already being used by power plants.

•      Sewer mining means taking what flows nearest the plant and treating it in the power plant

•      Benefits:

o   Waste heat from power plant used in MWTP processes.

o   Sludge from the power plant can be pumped as a slurry and then further dewatered with power plant waste heat and then injected in boiler.

o   Waste heat already being used to dry sludge (also lignite at Spiritwood).

o   Treated municipal wastewater used by power plant.

o   Net wastewater discharge of combo is zero compared to discharges from both without co–location.

o   Constructing a wastewater treatment plant addition in a separate location than main plant has geographic advantages (amount of sewer piping, lift stations, and pumps).

Can heating the Draw Solution in a Forward Osmosis ZLD System be a Beneficial Waste Heat Use?

Forward Osmosis (FO) holds lots of promise for many applications. Whether FO should be considered for any specific project will depend on:

•      Application specific details such as the solids content of the slurry and the availability of waste heat.

•      Approaches to regenerating the draw solution.

•      Process design and integration with RO and other sub-processes.

•      Membrane quality.
 

•      Product quality considerations.

There has been considerable effort to apply FO in direct competition to RO. To date, most of the success has come where FO has unique performance advantages such as use with high solids wastewater in power plant FGD systems and frac flow-back. Food applications where FO uniquely impacts product quality are also examples.

Oasys Water is transforming high salinity wastewater at the Changxing Power Plant. Oasys Water and its Chinese partner were selected to deliver the world’s first commercial application of Forward Osmosis (FO)-based ZLD at the state-of-the-art Changxing coal-fired power plant. Oasys provided its ClearFlo MBC system and pre-concentrating reverse osmosis (RO), while Beijing Woteer supplied physic-chemical filtration, ClearFlo Complete ion exchange pretreatment, and a crystallizer package.

•      Feed Water: The feed water at Changxing is a complex combination waste stream that includes flue gas desulfurization (FGD) blowdown wastewater and cooling tower blowdown (CTBD).

•      Results: Oasys Water’s patented technology is now transforming 630 m³/day of complex FGD wastewater at the Changxing Power Plant, reducing both the intake of local surface water and the outflow of industrial wastewater. This project has allowed Oasys to introduce an innovative FO-based brine concentration and water reuse process to treat desulfurization wastewater.

•      Economics: The draw solution recovery at Changxing was designed to use steam as the energy source, thus reducing overall energy requirements and overall cost. The Changxing system’s typical energy requirement is 90 kWh_t per m³ of processed wastewater.

In the FO Decision Guide we want to explore ways which energy for the FO can be supplied with waste heat from the power plant.

What about using a direct gas-to-liquid heat exchanger in the exhaust stack and  pump the draw solution through this exchanger?  It would reduce flue gas temperature as well as provide the FO energy.

What about using water in the exchanger and add MVR to bring it up to the right temperature?

Should Ethanol or Other Co-generation Candidates be Co-located at Power Plants?

•      The Blue Flint plant is co-located with Coal Creek Station, a GRE-operated plant near Underwood, ND. The synergistic relationship carries additional benefits in that the ethanol plant needs no boilers or their supporting infrastructure, maintenance, water treatment, and fuel costs.

•      This concept can incorporate beneficial use for the remaining flue gas heat.

•      The Spiritwood plant of GRE was built with the concept of co-generation for a grain drying operation and several other operations which could use waste heat.

Should operators of older plants consider converting their facilities into a manufacturing complex rather than shutting them down?

Should Recirculating Aquaculture Systems be Co-located at Power Plants?

•      Power plants can only reach 50/60 percent production efficiency, which results in a great deal of energy wasted in the form of heat.

•      Past research and aquaculture facilities tried to harness the waste heat of the cooling waters of power plants without much success.

•      The main cause of failure of these type of aquaculture systems was due to unregulated discharges of pollutants in the cooling waters or unplanned shut down of the plant resulting in sudden lack of heated water.

•      Modern technology is approaching the concept of using waste heat through the use of heat exchangers.

•      The use of waste heat in Recirculating Aquaculture Systems (RAS) for the culture of warm water species such as tilapia, perch, turbot, seabass, and eel could decrease running costs and increase the profitability of the venture.

•      Harnessing of waste heat decreases environmental impact of power plants and reduces the energy need of RAS facilities.

•      Waste heat might be successfully coupled with integrated aquaculture to achieve an environmentally, socially and financially sustainable enterprise.

•      This question is being addressed by a partnership between the Loughs Agency, Queen's University Belfast, and the University of Glasgow, supported by the EU's INTERREG IVA Program, managed by the Special EU Programs Body (SEUPB).

Air Conditioning and maybe even Ice from Power Plants

•      It appears that justifying the heat recovery is easy in the winter in cold climates but what about Indonesia, Vietnam and India where it is hot most of the year?

•       Co-generation with air conditioning would be one answer.

•      But what about areas that do not even have enough electricity to run air conditioners and are too distant to consider district cooling? Why not generate ice and deliver it by truck?  This is the way much of the U.S. dealt with the heat a century ago.

•      Many deaths in India recently were attributed to the extreme heat. So there is a lifesaving potential to this approach. Water is already being delivered by truck, why not ice?

Gus Shearer of Arvos volunteered that he had seen applications for air conditioning in India and will search for the background information to send to us.

Co-location of Greenhouse Farming is a likely Winner

Moshe Alamaro of MIT supplied information on the use of CO₂ and heat from coal and gas turbine plants for use in greenhouse growing. Tomatoes, for example, are increasingly grown in greenhouses rather than in ambient conditions. CO₂ levels well above the 400 ppm in the ambient atmosphere provide optimum growing conditions. Commercial greenhouses are routinely adding CO₂ to the greenhouse environment due to the fluctuation in CO₂ in the atmosphere locally. MIT has a unique way of using waste steam to heat the water to be used in greenhouse climate control and is looking for sponsors:  Contact Moshe Alamaro at alamaro@mit.edu

To listen to the recording click on FGD and Acid Gas Separation     104 minutes

The power point presentation is found at: Hot Topic Hour Slides     Acid Gas and Heat Recovery Slides