Under EPA’s Boiler MACT, treated wood, including railway ties, will not be able to be used as fuel in boilers after January 31, 2016. Some viable alternatives may be considered for the use of treated wood, including railway ties.
PH Haroz and Adam Haroz
Wood railway ties have been in use since the early 1800s when they replaced the then used stone railway ties. Through improvement of wood treating chemicals and technology, the useful life of railway ties have been prolonged to approximately 30 years, after which they are replaced. The aged ties, together with ties replaced due to derailment, are considered spent and up to now were typically used as fuel for boilers. Another source of treated wood is treated wood utility poles. There are roughly 135 million utility poles in service in the U.S. Approximately 4 percent of these poles are replaced annually.1
On January 31, 2013, the Environmental Protection Agency (EPA) published in the 40 CFR Part 63, the National Emission Standards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial and Institutional Boilers and Process Heaters (commonly known as Boiler MACT). Under Boiler MACT, treated wood, including railway ties, will not be able to be used as fuel in boilers after January 31, 2016. This article will attempt to provide alternatives for use of treated wood, including railway ties, if EPA’s Boiler MACT rule is not reversed.
Railway Ties Use
There are about 3,250 wood crossties per mile of railroad track, with more than 200,000 miles of railroad track used by railroads in the U.S. This equates to approximately 700,000,000 railway ties currently in use throughout the country. In 2013, approximately 19,000,000 ties were replaced by all U.S. railroads. This equates to 2.5 to 3 percent annual replacement rate of railway ties in the U.S.2
Wood crossties represent approximately 93 percent of the crossties used in North America. Railway ties are also made of concrete, representing about 6.5 percent market share. Steel or plastic/composite ties represent about 0.5 percent market share. According to a study conducted by ZETA-TECH Associates for the Railway Ties Association in 2006, wood railway ties’ costs per mile are 47 to 58 percent of the costs of concrete ties, 70 to 77 percent of the costs of plastic/composite ties and 68 to 77 percent of the costs steel ties.3 In the past, the spent wood railway ties were used as fuel for boilers to generate steam.
The Boiler MACT Rule
The Boiler Maximum Achievable Control Technology (MACT) Rule is the outcome of a long regulatory process, influenced by various court orders, that sets emission limits for industrial boilers and process heaters for various categories of emissions, with limits corresponding to what the EPA determines to be achievable with best available technology. The non-hazardous secondary material (NHSM) regulation under the Resource Conservation and Recovery Act (RCRA) identifies which non-hazardous secondary materials are, or are not, solid wastes when burned in combustion units.
NHSM that is not solid waste can be burned in boilers. NHSM that is solid waste can only be burned in a Commercial and Industrial Solid Waste Incinerator (CISWI). This includes boilers with additional pollution control and monitoring systems that are permitted as CISWIs.
The EPA has defined treated wood as a NHSM that is solid waste. The Treated Wood Council (TWC) and a coalition of nine other industry organizations submitted to the EPA petitions to allow treated wood to be considered NHSM that is not solid waste so it can be burned in boilers that are not CISWI. There are signals from the EPA that they may approve some of the treated wood to be considered NHSM that is not solid waste. Specifically, wood treated with creosote and at a later date, Disodium Octaborate Tetrahydrate (DOT) borate and Copper Napthenate may be considered NHSM that is not solid waste. TWC also petitioned the courts to overturn EPA’s NHSM rule on the grounds that EPA does not have the authority to regulate materials that are not discarded as waste. Treated wood used as fuel to generate steam is not discarded material.
EPA Approval Scenarios for Burning Treated Wood under Boiler MACT
Despite the EPA’s decision that treated railway ties and other treated wood products are to be considered NHSM that is solid waste (and therefore not able to be used as boiler fuel) there are still several scenarios that can play out:
- Scenario 1: The EPA will approve creosote-treated wood as NHSM that is not solid waste by the Boiler MACT compliance deadline of January 31, 2016.
- Scenario 2: The EPA will approve creosote, DOT borate and Copper Napthenate treated wood as NHSM that is not solid waste by the January 31, 2016 deadline.
- Scenario 3: Upon approval of creosote, DOT borate, and Copper Napthenate treated wood as NHSM that is not solid waste, environmental groups will challenge the decision, and it will be held up in court for an extended period of time. In the meantime treated railway ties would not be able to be burned in boilers as NHSM that is not solid waste.
- Scenario 4: Environmental groups will not challenge the EPA’s decision to consider treated wood with creosote, DOT borate, and Copper Napthenate as NHSM that is not solid waste.
- Scenario 5: The EPA will not approve any of the treated wood as NHSM that is not solid waste.
If scenarios 1, 2 and 4 happen, the treated railway ties will be allowed to continue being burned as NHSM that is not solid waste in boilers. If scenarios 3 or 5 occur, the burning of railway ties and other treated wood products in boilers in order to generate steam would have to cease. No matter the outcome of the ruling on creosote-treated railway ties, there are still railway ties and other wood products that have been treated with pentachlorophenol (penta) and copper, chromium arsenate (CCA) that do not seem to have a chance to be approved as NHSM that is not solid waste by the EPA. These types of treated wood will not need to be disposed of in some way other than by burning in boilers that are not CISWI.
Energy Value of Railway Ties
The potential energy of railway ties is based on the heat value of the wood, and the efficiency of the equipment that converts it to energy. A typical railway tie has a heating value of 8000 BTU/lb, and typically weighs approximately 150 pounds.2 From these values, the average railway tie can provide approximately 1,200,000 BTU of energy, which can be converted to 0.3516 Megawatt-hours (MWh) of electricity. The combined efficiency a power plant consisting of a boiler (75 percent efficiency), turbine (40 percent efficiency), and the electrical generator (98 percent efficiency), in the conversion process of the cross tie to electricity, yields an average efficiency of 29.4 percent.4 Based on the heat value of a typical railway tie along with the efficiency of the system, the burning of one railway tie can generate 0.1 MWh of electricity. According to the U.S. Energy Information Administration, in 2013 the average monthly electricity consumption for a U.S. residential customer was 0.909 MWh.5 Based on this statistic, along with the above calculations, nine railway ties can generate enough electricity to power one home for one month. Looking at that value, it can be derived that the burning of all of the 19,000,000 crossties replaced in the U.S. in 2013 could power 176,000 homes for an entire year.
Railway Ties Use Scenarios
This section will describe the alternative scenarios for using railway ties and other treated wood as fuel if these materials are considered NHSM that is solid waste and therefore, not allowed to be burned in boilers.
Scenario 1: Landfilling or Burning in CISWI Units
At the present time, the railroad companies are paying anywhere from $0 to $3 per tie as a tipping fee to the companies that prepare and sell the ties suitable to be fired in the boilers. If the ties have to be disposed of in landfills, and most likely only used for energy in CISWI units, the railroad companies may have to pay a tipping fee of $8 per tie (approximately $112 per ton) at an annual cost of $160,000,000.
Scenario 2: Conversion of Existing Boilers to CISWI
Some facilities that operate larger boilers, such as paper mills, could decide to convert their existing boilers to CISWI by installing additional pollution control and emission monitoring equipment and paying the permitting fees required for the conversion. This might be a feasible investment since the cost of $30 per ton for preparing the ties as boiler fuel will be offset by the tipping fee, which could exceed $100 per ton.
Scenario 3: Conversion of Out of Commission Power Plants Fueled by Coal to Railroad Ties Fueled CISWI Power Plants
This scenario shows the economic feasibility of converting out of commission power plants that were fueled by coal into power plants that can be fueled by biomass. Existing coal-fired power plants have material handling systems very similar to what would be required for feeding railway ties to the boilers. An example of a typical process flow diagram for the generation of power from spent railway ties can be seen in Figure 1, page xx.
Similarly to Scenario 2, the boiler’s owner can convert the boiler to a CISWI unit. This might be a feasible investment since the cost of $30 per ton for preparing the ties as boiler fuel will be offset by the tipping fee, which could exceed $100 per ton. If railroad companies were to join with boiler owners and/or power companies, the feasibility of using spent railway ties as fuel will improve.
Scenario 4: Build New Biomass Fueled CISWI Power Plants
Another option is to build new CISWI power plants that are able to be fueled by the spent railway ties (see Figure 1). The advantages of this scenario over the conversion of existing plants are as follows:
- They can be built in optimum locations and are not limited to locations of existing out of commission coal-fired powered plants.
- The components can be designed to the optimum size and operation for handling the railway ties as fuel.
Scenario 5: Others
There could be several other scenarios for use of railway ties and other treated wood. One example is gasification. Gasification is a process that converts organic or fossil fuel based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>1300 °F), without combustion, with a controlled amount of oxygen and/or steam. The resulting gas mixture is called syngas (from synthesis gas or synthetic gas).
A major challenge for railway ties gasification technologies is reaching an acceptable (positive) gross electric efficiency. The high efficiency of converting syngas to electric power is counteracted by significant power consumption in the waste preprocessing, the consumption of large amounts of pure oxygen (which is often used as a gasification agent), and gas cleaning. Another challenge becoming apparent when implementing these processes in real life is obtaining service intervals in the plants that are long enough not to require the plant to shut down every few months to clean the gasifier’s reactor.
Recommendations
It is recommended that the following action be taken to strengthen the case that treated wood should be categorized as NHSM that is not solid waste and to expedite alternate use scenarios of treated wood:
- Stack tests of emissions from the burning of different types of treated wood in typical biomass boilers used to generate steam should be conducted. These stack tests could be used to gather better data of the emissions from this activity. These should be conducted before the Boiler MACT deadline on January 31, 2016, after which it will be prohibited to burn treated wood in those burners. After the deadline, a lengthy process of obtaining permits from the EPA and the state will be required to conduct the tests.
The results of the emissions stack tests should be used to conduct atmospheric dispersion modeling. This type of modeling is a mathematical simulation of how air pollutants disperse in the atmosphere. It is performed using EPA software that solves the mathematical equations and algorithms, which simulate the pollutants’ dispersion and concentration at ground level. The models are typically employed to determine whether industrial facilities are or will be in compliance with the National Ambient Air Quality Standards (NAAQS) in the U.S. The results of the modeling would determine whether the burned treated wood results in emissions that are in compliance with NAAQS and would also determine the loading of toxins to the air.
- Prepare feasibility studies and business plans for the following scenarios:
- Conversion of existing boilers to CISWI
- Conversion of out of commission coal-fired power plants to treated wood-fired plants
- Construction of new treated wood-fired plants
- Other technologies that could use the railroad ties and other treated wood
The feasibility studies for these scenarios will provide the decision makers with the information and data required in order to determine whether any of the above mentioned scenarios are practicable.
Conclusion
The process of using crossties as a fuel source is not only an American one. The concerns regarding the burning of treated wood is also a hot button topic in Europe. Over 50,000 tons of crossties are incinerated for energy recovery every year in France. Despite the large number of crossties incinerated for fuel, Europe is currently in the process of researching the need to transition to using concrete crossties. At the end of 2010, members of the International Union of Railways approved the project “Sustainable Wooden Railway Sleepers” (SUWOS) in order to understand all of the alternative wood preservation technologies so that the use of hazardous chemicals, such as creosote can be limited if not eliminated.
The organizations that are affected by the potential banning of burning railway ties and other treated wood in boilers need to take action as described in the article to be prepared for the potential effect of the rule by January 31, 2016.
PH Haroz is President of Conversion Technology Inc. (Norcross, GA), an environmental and safety engineering consulting firm. He has Master’s Degree in Mechanical Engineering from the Georgia Institute of Technology. PH can be reached at (770) 263-6330 or e-mail [email protected].
Adam Haroz, EIT is an Engineering Manager at Conversion Technology Inc. He has a Bachelor’s of Science Degree in Mechanical Engineering from the University of California, San Diego. Adam can be reached at (770) 263-6330 or e-mail [email protected].
References
- Wood, A., Reddy, D. and Koganti R. (2008). The Environmental Impact of Utility Poles. ENGS 171.
- The Railway Tie Association. www.rta.org/faqs-main.
- Development of Comparative Cross-Ties costs and values by Zeta-Tech. rta.org/assets/docs/comparitive%20crosstie%20unit%20value%20%20costs.pdf.
- mpoweruk.com/energy_efficiency.htm.
- eia.gov/tools/faqs/faq.cfm?id=97&t=3.
- https://en.wikipedia.org/wiki/Gasification.