|
|
|
Home |
Coal-tar Residuals and the Environmental ThreatFormer manufactured gas plants typically operated 24 hours a day, 365 days a year. The solid and liquid residuals generated each day were a profound concern for the management of the works. The gas was only briefly stored, then distributed off the plant site. The residuals also had to be move along or they would constitute a space burden, an obstacle to movement around the gas yard, and the liquids would obstruct operations even more profoundly. Owners, operators and managers of gas works had a variety of available options before them. Some residuals could be utilized or sold as by-products and some residuals patently were valueless wastes. Today we are very much concerned about the gas making residuals that were deemed to be unsalable wastes by the works management. These wastes had particular physical and chemical characteristics that made them just as dangerous at the time of thei r creation as they are today. The smallest portion of the wastes were leaked and spilled in and around the works; the larger portion of the wastes that are found around the gas works today were subject to informed choices of disposition at the time of their creation, by the owners, managers and operators of each gas works.
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|
Typical residual coal-gas tar, after many years of weathering in |
Former Manufactured Gas Plants (FMGPs) produced toxic floaters, mixers, and sinkers, characterizing the variable density of the dominantly liquid wastes. Among these toxics were aromatic hydrocarbons, including the tar-acid phenols and cresols; the monocyclical aromatic hydrocarbons (MAHs) more commonly known as the BTEX series (benzene, toluene, ethylbenzene and xylene); the duocyclical aromatic hydrocarbons (DAHs) represented mainly by the base-neutral naphthalene; the polycyclical aromatic hydrocarbons (PAHs) represented by the medium and heavy oils (the "tars"), as well as various forms of cyanogens, sulfur, and some heavy metals concentrated from the trace metals of the coal and some of the enrichment oils.
Most coal-tar wastes are chemically labeled as "non-aqueous" because they do not have the high degree of solubility in water that has traditionally concerned chemists, who are not notably concerned about groundwater pollution. Taken from the standpoint of environmental protection, many of the wastes lie in the ppm range of solubility in water and, hence are chemicals of concern (COC) from the environmental standpoint.
Industrial chemical production, worldwide, was based on coal-tar as a source, from about 1854 (with Perkin's discovery of coal-tar dyestuffs) to the demise of coal as a routine domestic and industrial energy source, in the face of local municipal smoke and smog control ordinances (beginning in 1950s) and air pollution restrictions (1970 Federal Air Pollution Control Act). Certainly there are other factors, such as the rise of natural gas pipelines after the 1928 discovery of high-grade pipeline welding, the rise of petroleum refining as a source of road tar (after about 1940), and the general demise of our domestic steel industry (post-1965).
|
|
|
Gas Works No. 2 - Hannibal, Missouri |
|
|
|
Red sandstone was used to construct the 1870s coal gas plant at Ripley, Michigan, preserving the typical high arched windows typical of 19th century gas plants. (Photograph by A.W. Hatheway) |
Why coal-tar sites may go undetected until site explorationGeologists, geological, geotechnical, engineer and land survey crews are often in the key position to detect the presence of coal-tar residuals. The current standard of practice is that sufficient literature and records search work should be performed to detect the presence and layout of gas works over their operating lives.
|
|
|
(Click on Image for an enlarged image of the Sanborn Map) America's most famous prominent maker of fire insurance maps, the Sanborn Company, here visited the Mississippi River industrial and shipping community of Burlington, Iowa, in 1892 to depict its coal gas plant, built in 1856 by the future father-in-law of John D. Rockefeller. (From the Library of Congress collection) |
Generic FMGP Wastes Gas works wastes had to be managed literally on the day of their creation, burned as fuel, stored, recycled (as with some box wastes), treated (such as distilling for tar-oil fractions, ammonia or sulfur), dumped, transported and dumped, or discharged to the ground. Gas works management had to make a choice of waste management fate, as required by their circumstances, and the choice literally due on the day the wastes were created. Here follows a selection of actual gas works solid wastes typical of what will predictably be found at the dump or dumps of each former manufactured gas plant.
Generic FMGP Hazardous Substances |
||
|
Residual |
Origin in Manufacturing |
Present-Day Environmental Implication |
|
Coke |
Residuum of coal-gas coal charge |
Was always of value and could either be used ingeneration of carburetted water gas, for boiler or bench furnace heating, or sold to residents or businesses. May have sorbed contamination under certain FMGP conditions |
|
Ammonia |
Coal-Gas generation |
Generally dissipated over post-operational decades, but could emerge to endanger those involved in excavation or whom enter gaining leaks to sewers |
|
Scurf |
Clinker formed in retorts or gas generators |
Required retort chiseling to remove, or back-draft carbonization in carburetted water gas plants; should not be sorptive of PAH residuals |
|
Ash |
Refractive portion of retort or generator feedstock |
Low sorptive capacity for PAHs; Generally dumped around the plant or in off-site dumps |
|
Clinker |
Fused refractive portion of retort or generator feedstock |
Low sorptive capacity for PAHs; Generally dumped around the plant or in off-site dumps |
|
Liquor |
Washwater effluent from cleansing |
All forms tend to have dropped PAHs in tar form in surface watershed or subsurface aquifer matrix; Emulsions typically have a long, un-degraded life |
| Ammoniacal | From coal-gas manufacture | |
| Gas Liquor | From carburetted water gas | |
|
Tar |
PAH residue as a whole |
Any of such, when in the groundwater environment have the capacity to further contaminate bodies of ground water entering into contact with these gas-house wastes |
| Liquor | Water decanted by gravity from tar | |
| Tar | PAH residue as a whole | |
| Tar Sludge | PAHs containing ash | |
| Tar-Water Emulsion | Carburetted water-gas tars made with inferior non-coke feedstock and/or heavy oil enrichment | |
|
Lampblack |
Carbon sequestered from oil feedstock |
Most common in oil-gas processes; Very typical of Pacific Coast Oil Gas process; can occur with carburetted water gas and oil-enrich water gas. Formed without PAHs but acts to sorb such contamination afterward |
|
Scrubber Packing |
Generally wood chips |
Scrubbers commonly were packed with wood chips as a sorption medium |
|
Box Waste |
Media from purifying boxes, as removed and disposed of from standpoint of being spent and no longer capable of purification |
Always considered environmentally dangerous from standpoint of sorbed PAHs, cyanide, sulfur as well as arsenic and other heavy metals |
| Spent Lime | ||
| Spent Chips | ||
| Spent Oxide | ||
|
