4.2.1.3 Chemical Waste Incinerators
Dow Chemical Company
Midland, Michigan 48640
During the production of a variety of bulk organic chemicals, liquid wastes are produced and are incinerated by chemical manufacturers on their own sites. Many of these manufacturers produce chlorinated hydrocarbon products that require the same downstream technology for combustion products handling as is required for incinerating PCBs.
A Dow Chemical system was chosen as typical of these liquid waste incinerators since:
- Dow is seeking approval to burn contaminated wastes in the US;
- Dow practices liquid waste incineration in Canada; and
- data on the Dow incinerator at Midland, Michigan were readily available.
Collected liquid wastes are mixed, to balance heat content and viscosity prior to firing horizontally into a combustion chamber using air atomization (see Figure 3). Combustion air and secondary air are provided by a blower. The chamber is typically ~100 m3 in volume. Typical temperatures are in the 1100 to 1200 °C range with dwell times of the order of 2 seconds.
Freshwater is used initially to quench flue gases before they flow to a venturi scrubber and packed bed absorption system. In this section recirculating wastewater is used to scrub the effluent. Finally the effluent is sent to atmosphere through induced draft fans and a stack.
The Dow incinerator is designed to operate on liquids fed typically at ~32 kg/min PCB wastes that have been tested in these units are generally contaminated oils or contaminated waste streams. A support fuel, in this case natural gas, is used to preheat the unit and provide extra heat input as required. Products of the process are CO2 and H2O in the stack effluent and hydrochloric acid in the scrubbing wastewater. Scrubbing water would be treated centrally at most chemical sites prior to discharge.
Dow has been burning chemical wastes by this method of incineration for some time. There is no doubt that PCBs can be burned in this manner provided that the thorough mixing of the PCB liquid with a fuel takes place and modifications to existing scrubber and effluent water systems are properly carried out.
This system is only designed for liquid incineration but the possibility of introducing hammermilled capacitors as fluff could be viable.
In order to exemplify destruction efficiency reference is made to a similar incinerator owned by General Electric in Pittsfield, Massachusetts. In a pair of tests, waste oil containing 1.7% PCB was fed at 2-3 kg/min into their incinerator operating at 871°C and then 982°C. The PCB destruction efficiency was in the range 99.99 to 99.999%.
Waste incineration is a well developed technology. In the United States, there are over 200 liquid-injection incinerators in hazardous waste service similar to the one described above, most operating in conjunction with a commercial chemical production facility. (Some commercial waste destruction facilities do exist - roughly a dozen.) Companies marketing waste incinerators are said to number between 50 and 60 in the US although fewer than 30 have sold units.
Figure 3 Horizontally Fired Liquid Waste Incineration System (EPRI, 1979)
Click image to view a full size version.
The variations tend to centre around the technology of firing wastes into the combustion zone; subsequent scrubbing technology seems to be standard. Three such systems that are often referred to are:
- Prenco vertically fired liquid-injection incinerator;
- Vortex burner; and the
- Sudden Expansion (SUE®) burner by the Marquardt Company.
Prenco is typical of companies such as these; while they report 30 years of experience in the waste incineration business none of their units have been sold for PCB service.
The Vortex burner features tangential firing of fuel/wastes creating a more rapid heat release (1111 kW) than other systems.
Capital costs were estimated based on the Dow design and feed rates. They are comprised of those costs involved in storing and feeding PCB liquids to the unit and treating off-gases and scrubber water. Costs for the incinerator, land and laboratory are not included. The existing unit could be modified to suit PCB destruction at a capital cost of $1 630 000.
To operate this facility $2 930 000 per year, would be required. This includes cost on capital, maintenance, and utilities. The biggest expenditure would be for a mixing fluid, such as kerosene, which is added to the PCB liquid. No labour costs have been included as operators are presently available running the incinerator on other liquid wastes. The destruction cost per kilogram of PCB liquid would be $0.22.
The equipment required to modify an existing unit to burn PCBs is readily available. Land considerations could be a serious factor since a lagoon and other water treatment facilities would be required.
The impacts of this technology are minimal. The on-site nature of most operations is advantageous as the risk of moving the wastes elsewhere is minimized. Also, incinerators are often operated by knowledgeable technicians connected with a large chemical production facility giving them the experience and technical backup to operate efficiently. Public impact is minimized by their location and worker health and safety is usually well controlled at such facilities.
On-site or commercial scale chemical waste incinerators have been well accepted by regulators in the United States for PCB destruction. A summary of the approval of sites for PCB destruction in the US is given in Table 6. While most are dealing with contaminated oils the General Electric facility in Pittsfield, Massachusetts is evaluating concentrated feeds. With final rules now in place in the US it is apparent by the approved activity that facilities for incineration of PCB-contaminated fluids will be increasing substantially. |
