Cold-box process

In core-making shops, chemical scrubbers are in use. They use either acid (cold-box process) or basic (S02-process and Croning). The quantity of waste water discharged is dependent upon the accumulation of pollutants and salts in the circulating water. If pollution levels are too high, part of the polluted water must be drawn off. 

According to rough estimates, the use of this technique reduces the costs for core-making by 30 to 50 % compared to the cold-box process. 

Foundry moldings. In the auto, construction, machine parts, and steel industries, molten metal is poured into sand molds to produce the shapes of the products. The sand is bonded by phenolic resin, cured at 270°C. In the cold box process, the binder is phenolic... 

Cold-Box Process. In the cold-box process which takes place at room temperature, a gas catalyst is passed through the sand to promote curing. The catalysts are triethylamine or meth-ylethylamine for phenolic isocyanate binders, sulfur dioxide for vinyl-unsaturated urethane binders, and methyl formate for an alkali metal salt of a phenolic resole binder. Yii -ortho resins have been developed for the phenolic component by using water-free systems and salts of divalent metals as catalysts. A recent patent describes improvements in the two-package phe-... 

In chemical plants, turboexpanders are used to produce refrigeration for cold box installations. In all except energy recovery applications, there are gas-to-gas heat exchangers downstream of the turboexpander. Figure 6-14 recaps a process flow diagram of a natural gas processing gas plant. 

Figure 7 The spiral-wound heat exchanger (in front) to be built for the Snohvit LNG processing plant. The cold box measures 15x17 meter (footprint) having a height of 40 meter. The Statoil/Linde heat exchanger is the same type as the heat exchanger used in the Mossel-bay LNG plant in South Africa [17]. The lower tower (right) contains a plate fin heat exchanger for pre-cooling.

A simplified flow diagram for this segment of the process is shown in Figure 4, and thermodynamic analysis in Table III. The refrigerated exchangers and cold box represent about 30% of the lost work of the process. However, the tower itself has a very high percentage of the lost work in the system. Thus the details of the tower heat and material balance were examined in search of ways to improve its efficiency. 

A schematic diagram for the processing of synthesis gas to meet these three objectives using a combination upgrader/PSA unit is presented in Figure 9. A portion of the synthesis gas is diverted to the cold box for partial condensation and separation of the bulk of the methane and carbon monoxide from the hydrogen. The enriched (94-98%) H2 vapor fraction is reheated... 

Different foundry casting techniques are used. Included are plastic-based binders mixed with sand. Various types of molds and cores are produced that include no-bake or cold-box, hot-box, shell, and oven-cured. Usual binders are phenolic, furan, and thermoset polyester. There is the foundry shell casting, also called dry-mix casting. It is a type of process used in the foundry industry, in which a mixture of sand and plastic (phenolic, thermoset polyester, etc.) is placed on to a preheated metal pattern (producing half a mold) causing the plastic to flow and build a thin shell over the pattern. Liquid plastic pre-coated sand is also used. After a short cure time at high temperature, the mold is stripped from its pattern and combined with a similar half produced by the same technique. Finished mold is then ready to receive the molten metal. Blowing a liquid plastic/sand mix in a core-box also produces shell molds. 

Inlet gas enters the first cold box. Here the gas is chilled and separated liquids are passed to a large de-methaniser column. A second cold box repeats the process after which the cold gas is expanded to condense the remaining liquids. The cold gas is now passed to the top of... 

Cold box and refrigeration system. After the acid gas and water removal, the pyrolysis gas is cooled and condensed to approximately -165°C only hydrogen and some methane remain in the vapor phase. The feed locations are determined via process simulation. Hydrogen and methane are drawn from the lowest temperature stage separator and sent to thermal cracking furnaces as fuel. 

With the requirement for a direct production of, e.g., a H2/C0 = 1.0 gas, the SPARG process shows to be superior to conventional reforming. H2/C0 = 1 can be obtained with C02/CH = 1.5 and HgO/CH = 0.7. Without sulfur present, operation is possible with both ratios being ca. 2, which results in a larger reformer. On the other hand, the CH leakage at given pressure is smaller, which is advantageous if the cold box is replaced by other separation systems. 

Table 2.10 gives the relative share of the various core-making processes in German automobile foundries in 1991. This shows that the amine cold-box and hot-box systems dominate the market. Over 90 % of the automobile foundries use the amine cold-box system. The other processes (croning, C02-silicate) are mainly used for supplementary use, i.e. making cores with specific requirements (size, thickness,...). 

This process is commonly used to make cores of up to 100 kg and more, and small moulds. It provides a very smooth surface finish, and the dimensional accuracy is very high. The core removal properties are excellent and the sand can easily be reclaimed. This process is the most commonly used in core-making. An example cold-box core is shown in Figure 2.32. 

In a variant of the process called the Cold-box Plus process the corebox is heated to 40 - 80 °C using circulating hot water. This yields cores with even better mechanical properties, but results in higher interval times. 

Non-aromatic solvents can be applied in all processes using cold-box sand. The technique is relatively new and operational results as stated above need to be confirmed through repeated application. The technique has been implemented in foundries for the full range of automotive castings, as well as in castings for machinery, and in the construction and electronics industry. Both ferrous and non-ferrous applications are reported. 

In foundries, biofilters are applied for the removal of odorous gases, which mainly consist of amines from the off-gas from cold-box core-making processes and for the removal of VOCs (e.g. benzene) from casting shop exhaust gases. 

Iron casting (core production) For core production, the cold-box and Croning processes are used. Scrubbing concentrates are generated in amine scrubbing... 

The cryogenic process is considered by refiners to be less reliable than the PSA or membrane processes this is mainly due not to the process itself but to the need for feed pretreatments. Failure of the pretreatment system usually results in contaminants freezing in the cold box, leading to shutdown. 

---