US2972861A - Method of reducing the corrosive attack of combustion gases on metal - Google Patents

Description

Feb. 28, 1961 DAVIES 2,972,861

METHOD OF REDUCING THE CORROSIVE ATTACK OF COMBUSTION GASES 0N METAL Filed March 11. 1953 METHOD OF REDUCING THE CORROSIVE AT- TACK OF COMBUSTION GASES N lVmTAL Edward Brett Davies, Oldhnry, Birmingham, Englnnd, as-

signor to The Midland Tar Distillers Limited, Birming= ham, England Filed Mar. 11, 1953, Ser. No. 341,800 7 Claims. (Cl. 60-69.!)2)

It is well known that the products of combustion of fuels are corrosive and attack metal parts with which they come into contact. The corrosive agents are primarily sulphur compounds and the problem of corrosion is marked, for instance, with the products of combustion of petroleum oils, as these normally contain from 1 to 3% sulphur.

It is an object of this invention to provide a novel method of reducing the corrosive attack of combustion gases on metal.

Another object is to add certain special compounds to combustion gases for the purpose of reducing the corrosive attack of the gases on metals.

A further object is to reduce the corrosion of metal articles treated in metallurgical furnaces.

Yet another object is to reduce the corrosion in gas turbines and heat exchangers used therewith.

In my invention I reduce the corrosive attack of combustion gases on metal by introducing a tertiary amine or mixture of tertiary amines into combustion gases, or so introducing them into the combustion chamber as to become incorporated in the gases, before the gases come into contact with the metal parts. The amines and the point at which they are introduced must be such that, even if the amines are cracked, at least a substantial proportion of their lower homologues survives as a constituent of the gases. The amines may conveniently be used in the form of that fraction obtained in the distillation of coal tar which is commonly known as heavy coal tar bases, and we prefer to use such bases having boiling points between 250 and 350 C. 'Although their precise chemical composition is uncertain, they consist largely of the homologues of pyridine and quinoline.

I find that the presence of the amines (or possibly of the products of partial decomposition of the amines at the temperature of the gases) substantially reduces the corrosive attack on metal by sulphuric acid deposited from the gases. In general, of course, sulphuric acid is not present as such in the gases, but sulphur dioxide in the gases tends to be oxidized to sulphur trioxide and then to condense as sulphuric acid directly the temperature falls below the dewpoint of this acid. The invention is therefore particularly applicable to the protection of any metal surfaces which are at a temperature below this dewpoint. However, sulphur compounds are not the only cause of corrosion, and metal surfaces at a temperature above the dewpoint of sulphuric acid are also protected.

The amines may be introduced into the combustion chamber itself, provided that not all of them are de stroyed by burning; for instance, they may be introduced into a furnace at a point just short of the outlet from the furnace. Alternatively and preferably they are in troduced at a point outside the combustion chamber proper. 'What is essential is that they shall come into contact with metal with which the combustion gases come into contact and which tends normally to corrode. The amount of the amines required is only small.

The amines may be, and in general most conveniently required presents practical diiiiculties.

2,972,861 Patented Feb. 28, 1961 ice) are, introduced as such, but when the combustion chamher is small the introduction of the very'small amount These may be overcome by dissolving the amines in a solvent, e.g.' hydrocarbon oil or an aqueous solution of tartaric acid, or dispersing them in some other liquid diluent, to form a solution or mixture which can be introduced by spraying. A solution in oil may be introduced into the outlet end or colder part of a furnace, where the oil will partially burn to produce a reducing atmosphere in which some at least of the bases will continue to exist.

In theannexed drawings, Figure 1 shows diagrammatically how the amines can be introduced into a metallurgical furnace, and Figure 2 shows likewise how the bases can beintroduced in gas turbine plant.

Referring first to Figure 1, the furnace shown is used for heating billets, and comprises a long combustion chamber 1 in which oil from a burner 2 is burnt. The billets 30 are pushed through the furnace by a hydraulic ram 3 and withdrawn one at a time through a door 4 at the hot end of the furnace. The combustion gases, after flowing in countercurrent to the billets, leave through a flue S. The temperature in such a furnace decreases continuously from the burner to'the flue.

In this furnace the amines are introduced by, for example, a drip-feed device through a nozzle 6, which passes through the furnace wall at a point where the temperature of the billets is about 450 C. The amines therefore flow over billets which are at temperatures below the dewpoint of sulphuric acid condensed from the gases, and the corrosion and scaling of the billets is considerably reduced.

As another illustration of the practical application of the invention, the amines may be introduced into the transfer stage between a combustion chamber and a gas.

turbine driven by combustion gases from the chamber so as to protect the turbine and any subsequent heat-exchanger or other metal equipment from corosion. This is illustrated by Figure 2, which shows the turbine proper It] and the combustion chamber 11 from which the gas is fed to the turbine. Liquid fuel from a burner 12 fed through a pipe 13 is burnt in the chamber'll with air which is drawn through an intake 14 to a compressor 15 and forced by this through a heat exchanger 16 to the combustion chamber. The heat exchanger 16 is traversed by the hot gases from the turbine 10, which leave through a flue 17.

The gases in the transfer stage 18 between the combustion chamber 11 and the turbine 10 may be at a temperature between 500 and 600 C., which is much above the dewpoint of sulphuric acid. Even so, protection of the metal parts of the turbine can be obtained by injecting the amines into the transfer stage 18 at 19 by an injector diagrammatically shown at 20.

In many gas turbine plants the combustion gases are diluted with air or other gas in the transfer stage, and in such plants the diluting gas may be used to carry the amines to the turbine.

Of course, some of the amines may be decomposed or destroyed in a fast-moving stream of combustion gases at high temperature, but I have found that under such conditions as those prevailing in the transfer stage to a gas turbine a substantial proportion of amines survive.

Alternatively, or in addition, amines may be injected by an injector 22 into a gas turbine plant between the turbine and the heat exchanger, as shown at 21 in Figure 2, so as to protect the heat exchanger.

When the amines are used as such, and not dissolved or diluted, they may be introduced by volatilization from an asbestos or like wick projecting into the path of the combustion gases or of gases used to dilute the combusthe metal to be protected.

, tion gases, or by external vaporization with introduction of the vapour into either of these gases.

It is well known that tertiary amines commonly exist in coal tar fuels, and naturally if the combustion of such a fuel is incomplete small amounts. of amines may be found in the combustion products. In this invention the concentration of the amines in the gases is higher than is-ever produced by incomplete combustion of fuel. On the other hand, it is not necessary to use any substantial amount of amines. For example, in ya furnace burning 5,000 gallons of fuel oil per hour we may introduce into the back of the furnace 5 gallons per hour of light petroleum oil' or coal tar fuel containing 5% of heavy coal tar .bases. As another example, in a furnace burning a 'sulphurous gas at the rate of 3,000,000 cubic feet per hour, the rate of introduction of tertiary amines into the gases leaving the furnace maybe 1 gallon per'hour.

I claim: I

1. A method of reducing combustion gas acid corrosionof metals in a system where the metals are subjected to direct contact with combustion gases produced by the combustion of hydrocarbon fuels in a combustion chamber comprising the step of introducing into the products of combustion at a point outside said chamber but prior to contact with said metals at least one liquid tertiary amine, so that the amine is vaporized and is carried by the products of combustion into contact with 2. A method as in claim 1 wherein said amine is included in at least one heavy coal tar base. I

3; A method as in claim 2 wherein the range of boiling point of said heavy coalta'r base is within the temperatures of 250' to 350' C.

4. A method as in claim 1 wherein the liquid tertiary is introduced into the hydrocarbon combustion gases which flow through a gas turbine plant.

5.Amethodasinelaim4whereinsaidamineisintroduced into said hydrocarbon combustion gases during their passage through the transfer stage between the combustion chamber and the turbine.

6. A method as in claim 4 wherein said amine is introduced-into said hydrocarbon combustion gases be tween the turbine and a subsequent heat exchanger.

7'. A method of protecting metal surfaces below dewpoint of sulphuric acid within a combustion system, which metal surfaces are exposed to the products of combustion of hydrocarbon fuels containing sulphur, comprising the step of introducing at least one liquid tertiary amine into the combustion gases produced by the combustion of hydrocarbon fuels in a combustion chamber so that the amine is vaporized, carried with, the gases and comes into contact with the metal to be protected.

References Cited in the tile of this patent uNrrru) STATES PATENTS Great Britain Dec. s, 1938

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