Amines boilers

ALkylamines are corrosive to copper, copper-containing alloys (brass), aluminum, 2inc, 2inc alloy, and galvani2ed surfaces. Aqueous solutions of aLkylamines slowly etch glass as a consequence of the basic properties of the amines in water. Carbon or stainless steel vessels and piping have been used satisfactorily for handling aLkylamines and, as noted above, some aLkylamines can act as corrosion inhibitors in boiler appHcations. 

Fig. 11. Ocelot plant flow diagram. MEA, monoethano1 amine BFW, boiler feed water.

Moderately Volatile Ma.teria.ls, For moderately volatile materials, such as the amines commonly used in feedwater and boiler water chemical treatment, the distribution ratios vary from 0.1 to 30 for gases, the ratios are much higher. The distribution ratios of amines and organic acids are generally temperature-dependent. The distribution ratios for ammonia [7664-41-7] morpholine [110-91-8] and acetic acid [64-19-7] are shown in Figure 16 as examples. 

Steam and calcium hydroxide is formed. If the cooling water tends to form acid ia the boiler, either caustic or phosphate may be added to counteract the effect. When the cooling water tends to form base, only phosphate treatment is appropriate. Many dmm boilers that are operated on AVT have provision for phosphate or caustic treatment duriag condenser leaks because the amines used ia AVT have neither significant bufferiag capacity nor precipitate conditioning properties ia the boiler. 

At temperatures near the critical temperature, many organic degradation reactions are rapid. Halogenated hydrocarbons loose the halogen in minutes at 375°C (38). At temperatures typical of nuclear steam generators (271°C (520°F)), the decomposition of amines to alcohols and acids is well known (39). The pressure limits for the treatment of boiler waters using organic polymers reflect the rate of decomposition. 

The term steam quaUty refers to the amount of dry steam present relative to Hquid water in the form of droplets. The steam deUvered from the boiler usually contains some water. Excessive amounts can result in air entrapment, drying problems following exposure, and unacceptable steam levels (>3% water or <97% quaUty steam). Excessive amounts of water deposits dissolve boiler chemicals onto the load to be sterilized. Boiler chemicals are used to prevent corrosion in the lines. Inappropriate boiler chemicals, also called boiler amines, may introduce toxicity problems (see CORROSION AND CORROSION control). 

Overall comparison between amine and carbonate at elevated pressures shows that the amine usually removes carbon dioxide to a lower concentration at a lower capital cost but requires more maintenance and heat. The impact of the higher heat requirement depends on the individual situation. In many appHcations, heat used for regeneration is from low temperature process gas, suitable only for boiler feed water heating or low pressure steam generation, and it may not be usefiil in the overall plant heat balance. 

Amines or amides Alkyl amines (iindecyloctyl and diamyl methyl amine) polyamides (acyl derivatives of piperazine) Boiler foam sewage foam fermentation dye baths... 

Carbon dioxide, from the decomposition in the boiler of temporary hardness salts present in some waters, causes corrosion of steel steam pipework and cast iron valves and traps. Corrosion inhibitors may be used, but the choice of inhibitor must take into account the other materials in the system. Neutralizing amines such as morpholine or cyclohexylamine are commonly used. 

Boilers and steam systems Steel steam lines can be inhibited by the use of a volatile amine-based inhibitor such as ammonia, morpholine or cyclohexylamine introduced with the feedwater. It passes through the boiler and into the steam system, where it neutralizes the acidic conditions in pipework. The inhibitor is chemically consumed and lost by physical means. Film-forming inhibitors such as heterocyclic amines and alkyl sulphonates must be present at levels sufficient to cover the entire steel surface, otherwise localized corrosion will occur on the bare steel. Inhibitor selection must take into account the presence of other materials in the system. Some amine products cause corrosion of copper. If copper is present and at risk of corrosion it can be inhibited by the addition of benzotriazole or tolutriazole at a level appropriate to the system (see also Section 53.3.2). 

Amine and caustic solutions are used to remove these impurities. The amine solvents known as alkanolomines remove both H2S and CO, Hydrogen sulfide is poisonous and toxic. For refinery furnaces and boilers, the maxinaum HjS concentration is normally about 160 ppm. 

BOILER AND FEED-WATER TREATMENT Table 17.4 Properties of amines... 

The periodic development and use of new steel alloys can improve ferrous corrosion resistance however, where economizer units are constructed of copper alloys, under certain conditions serious copper corrosion problems may result. This occurs when FW having a pH over 8.3 also contains small amounts of ammonia and dissolved oxygen (DO). The ammonia may be present, for example, as a result of the overuse or inappropriate application of certain amines. Further damage may occur from the plating-out of the copper-ammonia ion then created as a cathode on boiler tubes. This promotes anodic corrosion of the immediate surrounding anodic areas. 

Ammonia (NH3) also may be present in some boiler systems, either by design or by the breakdown of amines, hydrazine, and other organic compounds. It attacks components and equipment constructed of copper and brass. 

In LP boilers with little returning condensate the requirement for MU is correspondingly high and may be relatively cool and partially oxygenated. Here it is not uncommon to observe the transport of ferrous bicarbonate [Fe(HC03)2] into the boiler (especially where no neutralizing amine is supplied) and the subsequent development of iron sludge, which settles on the top of combustion tubes and to the bottom of the boiler. 

Gunking This may occur when beginning the use of filming amines in condensate systems or polymeric sludge dispersants in FW systems. Here the new program may dislodge old corrosion debris or salt deposits and cause them to redeposit elsewhere (usually ultimately in the boiler section). 

Boiler scales and corrosion product deposits also may form from the thermal breakdown of treatment chemicals. Breakdown products of chemicals such as sulfite, amines, hydrazine, and chelants often are steam-volatile, and subsequent reactions may produce corrosion debris that forms deposits and causes blockages. This problem typically occurs when chemical treatments selected for use are applied under unsuitable operating conditions (as when the boilers are highly rated or raise steam at particularly high operating pressure or temperature). 

However, most smaller boiler plants do not do this rather, control usually takes place by curing the effect of corrosion by the use of various neutralizing and/or filming amines rather than by curing the cause. 

NOTE Neutralizing amines are often the first choice to neutralize carbonic acid in the condensate. In very small boiler plant applications they are... 

NOTE Some recirculation of ammonia and amine takes place within the overall boiler plant system, although at higher pH much of the ammonia is lost at the deaerator vent. In practice, this recirculation coupled with low er-than-theoretical C02 liberation (as a result of the incomplete breakdown of sodium bicarbonate when present in the boiler) typically results in a reduced amine-demand for any particular boiler pressure. This reduced demand, compared with the apparent demand, results in real cost savings. 

Recycled condensate often is of higher quality than FW, although in facilities with extremely long runs of steam and condensate lines, or where amine treatments are not used (e.g., some food processors, hospitals, drug manufacturers, etc.) and in high heat-flux power boiler plants, there is a tendency for the condensate to be contaminated by iron and smaller levels of copper. 

All-volatile programs (AVPs) These programs are employed in higher pressure boilers (generally power boilers) and utilize only volatile chemicals, such as ammonia, amines (such as diethylhy-droxylamine or DEHA), and other vapor phase inhibitors (VPIs). 

All preceding programs accept the conventional wisdom of operating within a control box of pH level and phosphate coordinates, despite the vagaries associated with BW sampling, amine contribution to pH and the omnipresent risk of hideout in utility boilers operating at high pressures. 

Feed points for AVT treatments vary, usually hydrazine is added to the base of the deaerator but it also can be added to the base of the condensate extraction pump. Ammonia (where used) or amine is injected into the suction side of the boiler feed pump. 

Where sodium sulfite is added as a component of multifunctional or one-drum products designed for smaller boilers, no cobalt catalyst is added because of the cobalt alkaline precipitation problem. Consequently, if the FW temperature is low this type of formulation is unsuitable because the sulfite requirement will be too high and the available reaction time too short. Probably a tannin-based, one-drum product would be more suitable (although here again there may be a problem because tannin-based products, unlike sulfite cannot be mixed with amines). 

As a result of the limited solubility of MEKO, it is often formulated with other boiler treatment ingredients such as filming and neutralizing amines, sulfite, or erythorbates, which permit increased concentration, improved stability, and better overall effectiveness. 

In lower pressure commercial and industrial boilers, handling and safety are issues of more concern than relative chemical effectiveness, and the fact is that because of such problems, ammonia simply is not used in these smaller plants. Caustic generally provides the necessary FW alkalinity and amines are then employed to overcome the problems of carbonic acid corrosion in the steam-condensate system. 

Under these conditions, because the neutralizing amine has no effect on oxygen ingress, it is common to supplement the neutralizing amine blend with a filming amine. Thefilmer may be applied separately (usually to a steam header) or blended with the neutralizers and added to the FW, or sometimes directly to the boiler. Care should be exercised when filmers are employed in previously corroded systems because it is very likely that old corrosion debris will be transported away to cause severe blockages in steam traps and valves. 

Morpholine is still the standard by which other amines are compared for pH control, and AMP has commonly been employed to control carbon steel boiler tube erosion-corrosion problems in European gas-cooled reactor stations. 

Ammonia is usually classified as a neutralizing amine because it provides post-boiler section corrosion inhibition through the same carbonic acid neutralization mechanism as regular amines. Similarly, hydrazine and other VOSs that produce ammonia, may be classified as functional neutralizing amines. 

The various functional properties of neutralizing amines, such as basicity, neutralizing capacity, DR, and volatility often have little or no direct relationship with each other, but all these properties are significantly different at boiler temperatures. This vital consideration is often insufficiently highlighted in manufacturers data sheets. Consequently, some of the commonly available information comparing amines records data at ambient temperatures, making it next to useless. 

Thus, when selecting amines for specific boiler cycle applications, any and all information provided should not be taken at face value, but should be carefully reviewed for relevance, in order to make the right choice and to ensure that proposed cost-benefits are realizable. 

Neutralizing capacity is not the only measure of a required amine feed rate. Once all acidic characteristics have been neutralized, amine basicity becomes the important issue because this raises the pH above the neutralization point, to a more stable and sustainable level. Consequently, in practice we are concerned with the level of amine necessary to raise the condensate pH to a noncorrosive level. This practical amine requirement is difficult to obtain from theoretical calculations because it must take account of the amine volatility, DR, and the boiler system amine recycling factor (as well as temperature). As noted earlier, the basicity of an amine has little or no relationship to its volatility or DR, so that reliable field results are probably a more important guide in assessing the suitability of an amine product than suppliers tables. 

Basicity is the ability of an amine to boost the pH level of an aqueous system in the boiler cycle to a level at which, under normal operating temperatures, the various materials of construction are reasonably stable. 

For larger boiler plants suddenly placed on high-fire and full-load conditions, the amine feed may need to be increased even where no increase in MU water is necessary. And for those steam generators using high-purity FW, particularly fine operational control may be required because maintenance of the correct pH within a very narrow range is usually a critical requirement, irrespective of temperature changes. 

In many of the largest boiler plants around the world AYT programs are often employed that commonly provide for hydrazine (as an oxygen scavenger) and a volatile amine such as morpholine (to boost the pH level). Where funds are limited, however, some facilities instead use ammonia as a pH booster because it is a low-cost item with a low equivalent weight and a high DR. Unfortunately, this approach may lead to downstream problems as ammonia becomes less chemically bound with increases in FW pH and a weaker base as temperatures rise. Consequently, a point is reached when ammonia ceases to further influence the pH level upward. 

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