Vacuum carbonate process

Coking produces a blast furnace coke feed substantially free of sulfur. However, the gaseous product, coke oven gas, has a sulfur gas content of 900-1, lOOg/m (at 15°C, 1 atm) [31]. This is mainly hydrogen sulfide, which may be removed either by the vacuum carbonate or Stretford processes. The sulfur gas removal efficiency of the Koppers Company s vacuum carbonate process is about 90%, which produces sulfuric acid, whereas the Stretford process can achieve 99% containment to a sulfur product (Chaps. 3 and 9). The choice of desulfurization process depends on the efficiency required and the sulfur product desired. Condensible hydrocarbons such as benzene (and other aromatics) and phenols have always been recovered by condensation, etc. [34]. 

Although the Vacuum Carbonate process is still commercially available, in recent years it has been replaced in many coke-oven gas treating installations by processes based on the oxidation of hydrogen sulfide to elemental sulfur in the liquid phase (see Chapter 9). 

Figure 5-39. Koppers two-stage Vacuum Carbonate process. Diagram courtesy of ICF Kaiser Engineers... 

Principal reactions occurring in the Vacuum Carbonate process are NajCOj + CO2 + H2O = 2NaHC03... 

Table 5-13 Vacuum Carbonate Process Solution Analysis ...

Table 5-14 Vacuum Carbonate Process Absorber Data ...

At plant A, the HCN that is removed in the Vacuum Carbonate process is recovered as a by-product. In most other plants, this substance is either removed and burned (to permit the H2S to be utilized in conventional acid plants), or it is destroyed in a specially designed sulfuric acid plant, which utilizes the H2S. 

Coke-oven gas normally meets tiiese specifications after it has passed through benzene washers. If the Vacuum Carbonate process is located ahead of the benzoie washos, which is... 

Analysis of Acid Gas From Plants Using Vacuum Carbonate Process ... 

A vacuum-retort process (Pidgeon process) was used during World War II for the production of magnesium and calcium. SiHcon, in the form of ferrosihcon, was used as the reducing agent instead of carbon to avoid the problem of cooling magnesium vapor in the presence of carbon dioxide ... 

The vacuum extraction process involves using vapor extraction wells alone or in combination with air injection wells. Vacuum blowers are used to create the movement of air through the soil. The air flow strips the VOCs from the soil and carries them to the surface. Figure 18.14 shows the flow diagram for such a process. During extraction, water may also be extracted along with vapor. The mixture should be sent to a liquid-vapor separator. The separation process results in both liquid and vapor residuals that require further treatment. Carbon adsorption is used to treat the vapor and water streams, leaving clean water and air for release, and spent GAC for reuse or disposal. Air emissions from the system are typically controlled by adsorption of the volatiles onto activated carbon, by thermal destruction, or by condensation. 

Vacuum carbonate An improved version of the Seabord process for removing hydrogen sulfide from refinery gases, in which the hydrogen sulfide is stripped from the sodium carbonate solution by steam instead of by air. Developed by the Koppers Company, Pittsburgh, in 1939 two plants were using this process in the United States in 1950. 

One typical example of carbon/carbon composite plates is that made by Oak Ridge National Laboratory (ORNL) in the United States [12]. The composite preform was fabricafed by a slurry-molding process from fhe mixed slurry befween short carbon fibers (graphite fibers were also added in some sample plates) and fhe phenolic resin. The mass rafio between fiber reinforcement and phenolic matrix is 4 3. The phenolic matrix improves the mechanical properties and dimensional stability of the plate. A subsequent vacuum molding process was utilized to fabricate composite plates and fluid fields with relatively high resolution (Figure 5.3, [11]). 

In this process liquid air is used for condensing the vapours in order to preserve the high vacuum carbonic acid has been used by other investigators, and Levene and van Slyke have recently employed sulphuric acid, cooled by a freezing mixture, as an absorbent for this purpose. 

Hot carbonates are well suited for the removal of C02 at moderate or high levels in the presence of little or no H2S. The process acquired its name from the use of elevated temperatures in both the absorber and the regenerator (110—115°C). Hot carbonates such as the Benfield and the Koppers Vacuum Carbonate utilize K2C03 to remove H2S, COS, and C02 from gas streams [35]. Their heat requirements and high solvent circulation make hot carbonates more expensive than other acid gas removal processes. Other hot carbonate processes, including the Catacarb and the Giammarco-Vetrocoke processes, use catalysts, corrosion inhibitors, and/or activators to enhance the removal of the acid gases. Hot carbonate-promoted systems are able to decrease the C02 level from 1% to 0.1%. Promoters include DEA, amine borates, and hindered amines [36]. 

In the CCC the filler is mixed with a resin, commonly phenolic resin, and sintered in a carbonization or graphitization step similar to the fabrication of synthetic graphite. The material obtained has a lower density, typically 20 0 % than synthetic graphite. The CCC allows the use of molding or vacuum molding processes. Lower plate thickness than synthetic graphite can be obtained. 

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