Carbonate fouling

When extremely poor control is exercised over lime-soda softening, the pH of the treated water can often rise and fall, and may rise to exceed pH 11.0 to 11.5 on occasion. This is clearly unacceptable and will dramatically increase the risk of carbonate fouling, thus tending to make subsequent treatment and control of the cooling system extremely difficult (on the premise that chemical and services treatment programs can be developed for almost any quality of cooling system makeup water, as long as the water quality remains reasonably consistent). 

The deleterious effect of water vapor was speculated to be due to its inhibition of carbon formation freeing the metal surface for interaction by H2S. Thus, sulfur poisoning of nickel at high temperature (above 673 K) may be more representative of a carbon-fouled surface, whereas at low temperatures it may be more characteristic of the clean metal surface. Again, this needs to be confirmed by direct measurements of carbon and sulfur adsorption. For Ni/Al203 and Ni/ZrOz the extent of sulfur deactivation was about fiftyfold at 673 K at 523 K the extent of deactivation was about 1000-fold. However, for Raney Ni the extent of sulfur deactivation was tenfold higher at 673 K than at 523 K this difference in behavior also needs confirmation and explanation. 

Operation of the desuperheating zone is particularly important. If the vapor leaving the zone is too hot, there will be carbon fouling of the fractionation trays. This temperature probably should not be above 700° F. The recirculated cooled slurry oil should not be too cool, however, because if it is as cool as 400° F, for example, the black oil will absorb some volatiles from the reactor product, leading to low flash points for the No. 6 fuel oil. 

From consideration of the thermodynamics of sulfur chemisorption on ruthenium (ref. 6), the gas phase sulfur activities (llgS/l ) of the lightly and moderately sulfur-poisoned Ru catalysts in equilibrium with the adsorbed sulfur at the process temperature (190 C), were approximately 0.02 and 1 ppb+ respectively. On the basis of these results, the equivalent partial pressure ratio for critical sulfur coverage is about 1 ppb at 490 C. This level is well below that attainable by conventional sulfur removal methods. Thus our result confirms the need for high performance desulfurization technology (ref 3) that can reduce sulfur contaminants in feedstocks to a sufficiently low sulfur level to avoid carbon fouling cf Ru/A Og steam reforming catalysts. 

Muller-Steinhagen, H. and Branch, C.A., 1988, Calcium carbonate fouling of heat transfer surfaces. Proc. Chemeca Conf Sydney, 101-106. 

The technical and economic optimization of such nickel catalytic filters has been the subject of various experimental investigations, which include studies of the effect of doping the catalyst with a second low-cost metal in attempts to improve its activity. In fact, it is well known that the formation of mixed Ni/Fe alloys can provide good resistance to carbon fouling [96]. Other transition metal catalysts, such as Co, are also known to be effective for hydrocarbon and bio-ethanol reforming [97]. 

Uses AntiscalanL desludger, and dispersant in industrial wafer treatment for use under severe caldum carbonate fouling conditions Regulatory FDA approved for use in sugar mills Australia AICS, Canada DSL, China IECSC, Japan ENCS, Korea KECI, Philippines PICCS listed Properties Colorless liw. si. odor misc. with water m.w. 2000 bulk dens. 10.21 lb/ gal vise. 50-100 Sp 1. cPs pH 2.8-3.6... 

Germany, the United Kingdom, and the United States shared ahke in the early development of stainless steels. In the United Kingdom in 1912, during the search for steel that would resist fouling in gun barrels, a corrosion-resistant composition containing 12.8% chromium and 0.24% carbon was reported. It was suggested that this composition be used for cutiery. In fact, the composition of AISI Type 420 steel (12—14% chromium, 0.15% carbon) is similar to that of the first corrosion-resistant steel. 

Physica.1 Properties. Carbonyl sulfide [463-58-1] (carbon oxysulfide), COS, is a colorless gas that is odorless when pure however, it has been described as having a foul odor. Physical constants and thermodynamic properties are Hsted ia Table 1 (17,18). The vapor pressure has been fitted to an equation, and a detailed study has been made of the phase equiUbria of the carbonyl sulfide—propane system, which is important ia the purification of propane fuel (19,20). Carbonyl sulfide can be adsorbed on molecular sieves (qv) as a means for removal from propane (21). This approach has been compared to the use of various solvents and reagents (22). 

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

Pretreatment of aqueous streams may be required prior to using ion exchange. Suspended soHds that can plug an ion-exchange unit should be reduced to the 10 p.m level. Organics that can foul resins can be removed by carbon adsorption. Iron [7439-89-6] and manganese [7439-96-5], commonly present in ground waters, should be removed because they precipitate on the resin. 

Pure carbon disulfide is a clear, colorless Hquid with a deHcate etherHke odor. A faint yellow color slowly develops upon exposure to sunlight. Low-grade commercial carbon disulfide may display some color and may have a strong, foul odor because of sulfurous impurities. Carbon disulfide is slightly miscible with water, but it is a good solvent for many organic compounds. Thermodynamic constants (1), vapor pressure (1,2), spectral transmission (3,4), and other properties (1,2,5—7) of carbon disulfide have been deterrnined. Principal properties are Hsted in Table 1. 

Charcoal—sulfur processes need low ash hardwood charcoal, prepared at 400—500°C under controlled conditions. At the carbon disulfide plant site, the charcoal is calcined before use to expel water and residual hydrogen and oxygen compounds. This precalcination step minimises the undesirable formation of hydrogen sulfide and carbonyl sulfide. Although wood charcoal is preferred, other sources of carbon can be used including coal (30,31), lignite chars (32,33), and coke (34). Sulfur specifications are also important low ash content is necessary to minimise fouling of the process equipment. 

Ethyleneamines are used in certain petroleum refining operations as well. Eor example, an EDA solution of sodium 2-aminoethoxide is used to extract thiols from straight-mn petroleum distillates (314) a combination of substituted phenol and AEP are used as an antioxidant to control fouling during processing of a hydrocarbon (315) AEP is used to separate alkenes from thermally cracked petroleum products (316) and TEPA is used to separate carbon disulfide from a pyrolysis fraction from ethylene production (317). EDA and DETA are used in the preparation and reprocessing of certain... 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

A test water box was installed during a 2-week trial to monitor corrosion and fouling in a utility cooling water system. A baffle plate from the test box was removed after the test. Small, hollow incipient tubercles dotted surfaces (Fig. 3.28). Small amounts of carbonate were present atop and around each tubercle. Each tubercle capped a small depression no deeper than 0.005 in. (0.013 cm) (Fig. 3.29). This indicated local average corrosion rates were as high as 130 mihy (3.3 mm/y). 

Figure 5.18 Heavily fouled and corroded internal surface of a galvanized carbon steel pipe.

Carbon residue, pour point, and viseosity are important properties in relation to deposition and fouling. Carbon residue is found by burning a fuel sample and weighing the amount of earbon left. The earbon residue property shows the tendeney of a fuel to deposit earbon on the fuel nozzles and eombustion liner. Pour point is the lowest temperature at whieh a fuel ean be poured by gravitational aetion. Viseosity is related to the pressure loss in pipe flow. Both pour point and viseosity measure the tendeney of a fuel to foul the fuel system. Sometimes, heating of the fuel system and piping is neeessary to assure a proper flow. 

Table 12-4 is a summary of liquid fuel speeifieations set by manufaeturers for effieient maehine operations. The water and sediment limit is set at 1% by maximum volume to prevent fouling of the fuel system and obstruetion of the fuel filters. Viseosity is limited to 20 eentistokes at the fuel nozzles to prevent elogging of the fuel lines. Also, it is advisable that the pour point be 20 °F (11 °C) below the minimum ambient temperature. Failure to meet this speeifieation ean be eorreeted by heating the fuel lines. Carbon residue should be less than 1% by weight based on 100% of the sample. The hydrogen eontent is related to the smoking tendeney of a fuel. Lower... 

Filter aids as well as flocculants are employed to improve the filtration characteristics of hard-to-filter suspensions. A filter aid is a finely divided solid material, consisting of hard, strong particles that are, en masse, incompressible. The most common filter aids are applied as an admix to the suspension. These include diatomaceous earth, expanded perlite, Solkafloc, fly ash, or carbon. Filter aids build up a porous, permeable, and rigid lattice structure that retains solid particles and allows the liquid to pass through. These materials are applied in small quantities in clarification or in cases where compressible solids have the potential to foul the filter medium. 

Chemical scaling is another form of fouling that occurs in NF and RO plants. The thermodynamic solubility of salts such as calcium carbonate and calcium and barium sulfate imposes an upper boundary on the system recovery. Thus, it is essential to operate systems at recoveries lower than this critical value to avoid chemical scaling, unless the water chemistry is adjusted to prevent precipitation. It is possible to increase system recovery by either adjusting the pH or adding an antisealant, or both. 

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