Waste to Wealth with KVT
Florian Kanzler
Business Development
KVT Process Technology

Sebastian Skene
Business Development
KVT Process Technology

The article shares insights on KVT process technologies that help various industries to recycle and valorise waste and creating wealth of it.

Kanzler Verfahrenstechnik (KVT) strives to upgrade processes to aid their customers in the struggle of competing in an accelerated world where economic and ecologic pressures have never been higher.

An increased demand for technologies encompassing recycling of wastes, waste valorisation and integrated continuous solutions has been observed in three areas:
  • Sulphur-containing exhaust gases
  • High TOC sludges
  • Waste brines
Sulfuric acid is the most widely used and consumed inorganic acid. Pure sulfuric acid is a highly corrosive, colourless, viscous liquid. Growth rates in consumption are at 4-5% per year. Its consumption is an indicator of the development of chemical industry in a country. Today there is practically only the contact process for production of Sulfuric Acid.

The sulfur dioxide used in the sulfuric acid plants typically comes from:
  • Combustion of elemental sulfur
  • Roasting gases from sulfide ores Pyrite FeS2 (as sulfur source for this purpose removed intentionally), as a by-product from the smelting of copper ore (CuFeS2, Cu2S, CuFeS4), zinc and lead ores (ZnS, PbS) and others (Ni, V, Mo ...)
  • Sulfur cleavage of sulfates or sulfuric acid waste
WET SULFURIC ACID TREATMENT
Fur ther, there is also the possibility to recover sulfuric acid from various off-gas streams. The OXYSULF Technology is used for waste gas desulfurization with recovery of pure, concentrated sulfuric acid. The OXYSULF process can handle wet gases containing sulfurous components such as H2S, CS2 and SO2 to convert them to sulfuric acid. In a world where the ecological aspect needs to be integrated with efficiency and profitability, this process technology created a space for itself : sustainability with guaranteed emissions go together with the economical convenience.

Sulfur containing exhaust gases can originate from various sources. KVT originally developed this wet process to produce sulfuric acid from off gas containing sulfur bearing compounds for a viscose production company in 1992. Ever since, the field of application has grown and with every new requirement, solutions were found which where integrated in the core of the technology. Nowadays it is applicable in:
  • Refineries & Petro-chemical Industr y (SRU)
    • After the Gas Sweetening Unit based on amine wash system
    • After Sulfur Burner in sulfuric acid production plants
    • Spent acid regeneration after the alkylation phase which uses sulfuric acid
  • Coal based Fer tilizer and Chemical Industry (Syngas SRU)
  • Cokes Manufacturing
    • Coke oven gas treatment
  • Non-Ferro Metallurgical Industr y (Mo, Pb…)
    • Off-gas treatment coming from metal roasters
  • Power Industry
    • Off-gas coming from sulfur recovering unit for burning pet coke
    • In the Sulfur Recovery Unit in IGCC Plant
  • Viscose Industry
    • Off-gas coming from the spin bath unit and from spinning machine as well as from the CS2 production plant that can be linked to the viscose production plant.
  • Natural Gas Processing
    • Treatment of acid gas coming from the sour gas treatment unit
    • Tail gas treatment of Claus Process
Process
The OXYSULF Process is a customized, highly energy efficient technology used for cleaning wet waste gases (no preceding drying step process is required) containing sulfur compounds, that produces a sallable product: sulfuric acid.

The process is based on the Catalytic or the combination of Thermal and Catalytic Conversion of sulfur-bearing compounds into sulfuric acid. It is able to handle contaminants such us SO2, H2S, COS or CS2, at a wide concentration range.


OXYSULF Wet Sulfuric Acid Plant

The following reactions and processes take place in the plant:


The off-gas passes over the Gas Conditioning System that can be a prefilter, a scrubber, Dryf-Fil hot gas filter or a preheater (KVT Exclusive), depending on the raw gas compositions and concentrations.

For low concentration (with a low calorific value of the gas) in order to reach the operating temperature of the catalyst, the stream gas needs preheating. The preheating is par t of the Gas Conditioning System and takes place through the Heat Recovery System that recovers the excess heat from the condensation column and from the reactor.

For high sulfur compounds concentrations, the first step is done with a combustion chamber where the thermal oxidation to SO2 takes place. In order to reach the operating temperature of the catalysts, the gas stream passes as team generator. The steam generator (Waste Heat Boiler) is part of the Heat recovery System that recovers the excess heat from the condens ation column, from the reactor and after the combustion chamber.

The gas passes over the reactor with multi-bed catalysts, where the Catalytic Oxidation of sulfur compounds to SO3 takes place. Optionally, in the first catalyst bed of the reactor, a DeNOx catalyst converts the NOx with the upstream added NH3 to N2. Secondly, a noble -catalyst conver ts SO2 par tly to SO3 . This exothermic process increases the gas temperature fur ther above 400°C. The following catalyst bed(s) contain(s) a V2O5 - catalyst which conver ts the remaining SO2 to SO3. The resulting SO3 together with the water vapor in the off- gas forms gaseous sulfuric acid.

Downstream of the reactor, a finned tube heat exchanger cools the gas close to condensation point of sulfuric acid, which typically is 250°C. The heat transfer medium in the finned tube heat exchanger is liquid salt, which is used to preheat the off gas.

The gas containing gaseous sulfuric acid enters the concentration column, where it is cooled to about 70°C by passing over the tube side of the glass tubes, in which a heat exchanger for preferred use is integrated. Sulfuric acid condenses and gets concentrated up to 99%, while running counter-flow against the hot gas.


THERMODEC - Sludge Treatment Plant

The gas leaving the concentration column at the top contains sulfuric acid mist, which is precipitated in the downstream wet electrostatic precipitator (WESP). The acid mist collected in the bottom of the WESP, having a typical concentration in the range of 50%, is injected into the top of the condensation column to get highly concentrated acid. A second reactor stage makes possible to obtain sulfur oxidation efficiency up to 99.8% and recovery of sulfur as 99.7% sulfuric acid. The tail gas complying with the current international emissions regulations is discharged to the atmosphere through the main stack.

Each plant is customized for the different customer's requirements. Generally, the type of OXYSULF technology to be used is dictate by the off -gas sulfur compounds concentration. The carbon absorbs un-reacted SO 2 and oxidizes it to SO3. The SO3 is washed out with demineralized water from the activated carbon to form weak sulfuric acid. This acid is collected and reinjected into the gas stream entering the WESP. This cools the gas further and increases the acid concentration.

Advantages
The existence of a technology, enabling the operators to produce sulfuric acid additionally to improving off gas quality, has been a welcomed tool in boosting plant figures, besides optimising efficiency and lowering costs. It simultaneously improves environmental impact, corporate social responsibility and economics.

SLUDGE TREATMENT
Sludges of all kinds pose a problem to operators. Often expensive disposal contracts burden other wise well- designed production sites. The alternative of energy consuming drying has been extended to thermal decomposition, able to treat sludge under the aspect of energy recovery and in cases recovery of materials. Originally developed for Glycerine MONG (matter organic non Glycerine), the area of application now encompasses resin production and many other industrial sludges. The technology has the advantage of separating solid compounds from challenging sludge streams, generating energy and allowing for recycling of sludge components (salt, carbon black … ) or gaseous components. The vapor stream and the remaining system gas - if applicable-to gether with other waste gases can be fed into an incinerator to provide full oxidation of the combustible compounds. If required, liquid or gaseous waste streams from other sources can also be added to the incineration unit. Organic compounds are conver ted to H2O and CO 2. Sludge disposal costs can vary with geographic location, whilst the loss of material with potential for recovery is often neglected altogether in calculations. Production sites are dependent on disposal service providers and their prices.


SEABRINE Waste Brine Treatment Plant

Process
The sludge is conditioned and pre - dried using the processes own energy and heat. It is then fed into the THERMODEC reactor which is operated at optimal conditions between 300-500°C. Here the thermal separation of the organic components takes place. The mixture separates into a gas phase and a dry solid phase. The gas flows into the combustion chamber. D epending on the composition, the dry product stream can be fur ther treated in the residue treatment or easily disposed of if it is not suitable for recycling itself. Depending on the field of application even the gas can be fur ther treated for increased recovery of valuable substances.

WASTE BRINE TREATMENT
Originating from the Epichlorohydrin Production from Glycerine, brine purification is now a technology used to treat salt containing waste waters from many different origins. An especially beneficial synergy can evolve, when a chlor-alkali electrolysis is near a chemical production site with large volumes of waste brines. In this case the chemical producer saves disposal costs, and the elec trolysis operator gains access to ensured and inexpensive water supply.
Process
First pH-levels are adjusted with HCl. The brine is then fed into a high -pressure part where the reaction takes place together with the catalyst and oxygen. Here hydrocarbons and chlorinated hydrocarbons are oxidized. Due to the exothermic nature of the reaction, energy and heat can be used to sustain the process itself and for external use. After decompression the formed vapor is condensed. Finally, the catalyst is separated for reuse.

Reaching low TOC values < 7 The process is especially well suited for high TOC brines with critical components which complicate traditional biological treatment or crystallisation. Where a biological treatment, which would require a dilution factor of 20-50, or a high chemical consuming multistage cleaning process after crystallisation fail to deliver proper solutions, this process valorises a classical waste stream.

Conclusion
KVTs own technologies OXYSULF, THERMODEC and SEABRINE aim at reducing waste, increasing efficiency and recycling all possible parts of typically cumbersome and expensive to manage waste streams. Often dismissed sources for energy and recyclable resources are exploited tapping in the synergy of unusual solutions approaches.