Double contact

In the early 1970s, air pollution requirements led to the adoption of the double contact or double absorption process, which provides overall conversions of better than 99.7%. The double absorption process employs the principle of intermediate removal of the reaction product, ie, SO, to obtain favorable equiUbria and kinetics in later stages of the reaction. A few single absorption plants are stiU being built in some areas of the world, or where special circumstances exist, but most industriali2ed nations have emission standards that cannot be achieved without utili2ing double absorption or tad-gas scmbbers. A discussion of sulfuric acid plant air emissions, control measures, and emissions calculations can be found in Reference 98. 

Implementation of cleaner production processes and pollution prevention measures can yield both economic and environmental benefits. The following production-related targets can be achieved by measures such as those described above. The numbers relate to the production processes before the addition of pollution control measures. In sulfuric acid plants that use the double-contact, double absorption process, emissions levels of 2 to 4 kilograms of sulfur dioxide... 

Maximize the recovery of sulfur by operating the furnaces to increase the SO, content of the flue gas and by providing efficient sulfur conversion. Use a double-contact, double-absorption process. 

Contact Sulfuric Acid Process Monsanto, Parsons, Davy Powergas, others Can accept elemental sulfur, or H2S and S02-bearlng streams down to about 5Z sulfur content A double contact/double absorption plant can recover up to 99.8Z of the sulfur fed to it. All sulfur compounds handled... 

Sulfuric Acid Options - To meet current standards, sulfuric acid plants must generally be designed as double-contact, doubleabsorption plants (6), or they must use a tail-gas scrubbing step to generate an alternate product, e.g., ammonium sulfate. 

Q2. Double contacts on the bottom of the relay independent of each other under the coils, and double on top but with a pivot point in the middle of the two coils. 

Second lau analysis is applied to a 100 tonnes per day double-contact double-absorption (DC-DA) sulphuric acid plant in order to bring out true energy conversion efficiencies and consumptions based on uork availability of various streams. Second lau efficiencies are compared uith those of first lau to pinpoint true losses and inevitable consumptions in energy conversion processes. 

Fig. 1.4. Double contact sulfuric acid manufacture flowsheet. The three main S02 sources are at the top. Sulfur burning is by far the biggest source. The acid product leaves from two H2SO4 making towers at the bottom. Barren tail gas leaves the final H2S04 making tower, right arrow.

Fig. 9.1. Single contact H2SO4 making flowsheet. SO3 rich gas from catalytic SO2 oxidation is reacted with strong sulfuric acid, Reaction (1.2). The reaction consumes H20(f) and makes H2S04(f), strengthening the acid. Double contact H2SO4 making is described in Fig. 9.6. A few plants lower the SO2 content of their tail gas by scrubbing the gas with basic solution (Hay et al., 2003).

Fig. 9.6 is a flowsheet for double contact H2S04 making. It shows ... 

Double contact acidmaking oxidizes its S02 more completely to S03 than single contact acidmaking. For this reason it ... 

Plant SI (double contact) iiuni-ow3 [Jiaina. uic uaia aiw iui M2 (double contact)... 

Cumerio 1 (double contact) Cumerio 2 (double contact) M5 (single contact)... 

Most sulfuric acid plants are double contact plants, Fig. 9.6, Tables 9.3, 19.3 and 23.2. They efficiently oxidize their feed S02(g) to S03(g) and efficiently make the resulting S03(g) into H2S04(f). Single contact plants (Fig. 9.1) are simpler and cheaper - but less efficient. 

Most of the mathematical chapters analyze catalytic SO2+/2O2-> S03 oxidation in single and double contact acid plants. The remainder examine temperature control and H2S04 making. 

The process is called double contact acidmaking because gas and sulfuric acid are contacted twice, steps (b) and (d). 

Fig. 19.1. Schematic of 3-1 double contact sulfuric acid plant. The plant consists of ...

The increase in % SO2 oxidized after each bed is notable. Other industrial versions of double contact acid plants are ... 

Double contact acidmaking always gives more efficient S02 + AO 2 - S03 oxidation than single contact acidmaking. This leads to ... 

The reason for double contact s high S02 oxidation efficiency is given in Figs. 19.6 and 19.7. 

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