Waste feed

During the conceptual design it is necessary to establish what constitutes waste feed. The waste feed characteristics and the relative volumes of the different waste categories to be incinerated will probably affect the selection of the combustion technique and also the basic concept of the off-gas treatment system. The distinct categories of wastes that may affect the design or selection of the incineration system are as follows  

The amount and type of pretreatment, if any, shall be established in the conceptual design of the incineration system. The waste preparation or pretreatment 

Depending on the particular design of the overall incineration system (including the off-gas treatment system), some of the items or batches of waste having any of the following characteristics may have to be excluded from or minimized in the waste feed  

It is necessary to establish early in the conceptual design whether acid gas forming materials (e.g. halogenated or sulphur compounds) should be included or eliminated from the waste feed. If included, the system must be capable of processing these materials and the resulting combustion products. 

Waste sorting should be done to the extent possible at the place of waste generation. If this is not possible the incineration facility shall have a sorting area where material not suitable for incineration can be removed. Depending on the radioactivity level of the wastes and the potential for airborne contamination, the wastes may or may not be sorted by hand. Alpha bearing wastes shall be sorted in a sealed glove box. 

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Control Systems. Control systems are used to regulate the addition of Hquid waste feed, auxiHary fuel, and combustion air flows to the incinerator furnace. In addition, scmbber operation is automated to help ensure meeting emission limits. Flows are measured using differential pressure... 

If a waste contains a mixture of volatile components that have similar vapor pressures, it is more difficult to separate these components and continuous fractional distillation is required. In this type of distillation unit (Fig. 4), a packed tower or tray column is used. Steam is introduced at the bottom of the column while the waste stream is introduced above and flows downward, countercurrent to the steam. As the steam vaporizes the volatile components and rises, it passes through a rectification section above the waste feed. In this section, vapors that have been condensed from the process are refluxed to the column, contacting the rising vapors and enriching them with the more volatile components. The vapors are then collected and condensed. Organics in the condensate may be separated from the aqueous stream after which the aqueous stream can be recycled to the stripper. 

Process problems include slag formation, ash removal, and process control because of the heterogeneous solid waste feed. These problems have been managed to some degree by "overdesigning" the plant, with the result that combustion of municipal solid waste is not economically competitive in areas where low-cost electricity or landfills for waste disposal are available. The future cost of electricity is difficult to predict. However, the steady decrease in the availability of landfills portends increasing use of this process to dispose of municipal wastes, particularly in large cities. 

Owners or operators of MACT units must ensure that the MACT emission standards are not exceeded. To do this, the unit must operate under parameters that are demonstrated in a CPT. The unit s operating parameters, such as temperature, pressure, and waste feed, are then set based on the result of the CPT and documented in a NOC. Continuous monitoring systems are used to monitor the operating parameters. 

Monitoring the combustion temperature and hazardous waste feed rate. 

Testing the emergency waste feed cutoff system and associated alarms. 

In addition, during the startup and shutdown of an incinerator, hazardous waste must not be fed into the unit unless it is operating within the conditions specified in the permit. An incinerator must cease operations when changes in waste feed, incinerator design, or operating conditions exceed the limits designated in its permit. 

The purpose of a hazardous waste incinerator permit is to allow a new hazardous incinerator to establish conditions including, but not limited to, allowable waste feeds and operating conditions that will ensure adequate protection of human health and the environment. The incinerator permit covers four phases of operation pretrial bum, trial bum, posttrial burn, and final operating conditions. 

During operation, the owner/operator of an incinerator must conduct sufficient waste analyses to verify that the waste feed is within the physical and chemical composition limits specified in the permit. This analysis may include a determination of a waste s heat value, viscosity, and content of hazardous constituents, including POHCs. Waste analysis also comprises part of the trial burn permit application. U.S. EPA stresses the importance of proper waste analysis to ensure compliance with emission limits. 

Monitor the combustion temperature, the waste feed rate, and the indicator of combustion gas velocity on a continuous basis. 

Test the emergency waste feed cutoff system and associated alarms at least weekly unless otherwise directed by the Regional Administrator—as a minimum, operational testing must be conducted monthly. 

Tier I The focal point of Tier I is the waste feed. This tier limits the hourly feed rate of individual metals into the combustion device. These limits have been developed by U.S. EPA and can be found in Part 266, Appendix I.5 U.S. EPA established these feed rate limits by considering flue gas flows, stack height, terrain, and land use in the vicinity of the facility. It determined acceptable air quality levels for each type of metal as a function of terrain, stack height, and land use in the vicinity of the facility. This value is also the waste feed rate, as Tier I assumes that 100% of the metals that are fed into the unit will be released into the atmosphere. 

The final emission standard under the BIF regulations limits the unit s output of HCI and chlorine gas (Cl j). These compounds combine with water in the air to form acid rain. They are also a known cause of human respiratory problems. The emission controls are implemented in the same way as the metal emissions, using the tiered approach. The owner/operator has a choice of three tiers with varying focal points. The Tier I and Tier II screening levels for waste feed and stack emission limits are located in Part 266, Appendices II and III.5... 

In addition to the standards described above, the BIF owner/operator must fulfill requirements for establishing an automatic waste feed cutoff system. The facility must also conduct inspection and monitoring, maintain certain records, and close in accordance with given regulations. 

Hazardous waste feed restriction of 3.0 ppmw and 120 pg/dscm maximum theoretical emission concentration (MTEC) or 120 pg/dscm total emissions... 

Mercury 8.1 pg/dscm Hazardous waste feed restriction of 1.9 ppmw and 120 pg/ dscm MTEC or 120 pg/dscm total emissions 120 hazardous waste MTEC feed restriction or 120 pg/dscm total emissions 11 pg/dscm 1.2 E-6 lb/MMBtu or 6.8 pg/ dscm depending on Btu content of hazardous waste TCI as surrogate... 

Plasma gasification is a generic-type process that can accommodate virtually any input waste material in as-received condition, including liquids, gases, and solids in any form or combination. Also, moisture content is not a problem. Liquids, gases, and small particle-size waste materials are very easily and efficiently processed. Bulky items, such as household appliances, tires, and bedsprings, can also be readily accommodated without loss of destruction efficiency. The reactor vessel and waste feed mechanism are designed for the physical characteristics of the input waste stream. Even waste materials such as low-level radioactive waste can be processed to reduce the bulk and encapsulate the radioactive constituents to reduce leachability. 

Plasma destruction of transformer oil with PCB absorbed in sites was investigated in two ways of the waste feeding. In the first experiment the sample was washed up with a solvent and the fluid extract was then... 

Silver content of anolyte circuit (AgN03) makeup rate —Waste feed cutoff tied to current flow —Temperature of anolyte feed tank (main concern is precipitation of by-products)... 

Waste feed rate to anolyte cell —Maximum particle size... 

First, the incinerator must achieve a destruction and removal efficiency (DRE) of at least 99.99% for each of the designated Appendix VIII chemicals present in the waste feed. In other words, 0.01% of the respective compound in the waste feed can be emitted in the incinerator stack gases. The specific Appendix VIII chemicals evaluated are selected by EPA from those found in the hazardous waste at reasonable concentrations and are termed principal organic hazardous constituents (POHCs). 

Tests have been conducted on wet and dry cement processes in the United States, Canada, Sweden, and Puerto Rico for wastes containing a wide range of chlorinated chemicals, including PCBs (13-16). Generally, the DKEs have been found to be in the range of 99.99%, with no adverse impact on product quality or plant operation if chlorine addition is restricted to less than 1% of the net fuel/waste feed. DKEs of less than 99.99% have been observed, however, where poor control of combustion air exists and waste is inadequately atomized, even when an acceptable cement product is being produced. 

Many site-specific characteristics have an impact on vitrification technologies. One critical aspect of any thermal technology is the water content of the waste. Water dilutes feed material, requires energy to drive off, and physically limits the feed rate of waste. Feed preparation is another variable, which differs with the technology and with site-specific characteristics. Many estimates do not take into account site preparation and waste disposal costs. Only complete treatment life-cycle assessments can provide reliable comparison data, and such studies are, by definition, highly site and waste specific (D18248T, p. 55). 

CF Systems extraction process removes a broad range of contaminants and typically extracts more than 99% of the organic contaminants from the waste feed. However, the CF Systems process cannot remove heavy metals or other inorganics. Also, the CF Systems process does not destroy the organic contaminants in soil or waste but rather extracts them from the medium in which they are contained. 

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