Sodium hydrogen carbonate, known as sodium bicarbonate (NaHCO3), is the main reagent used in the SodaFlexx Exhaust Gas Cleaning System. SodaFlexx utilises its powder form to neutralise SOx pollutants in exhaust gases. It is easy to handle due to its favourable chemical characteristics:
Sodium bicarbonate can be sourced by two methods:
1. Synthetically using the Solvay™ or ammonia-soda process
2. Mined from natural deposits of Trona and Nahcolite
The Solvay process is a manufacturing method that heats limestone to produce calcium oxide and carbon dioxide. The carbon dioxide is then placed in a solution of ammonia in a salt brine, and this generates an ammonia bicarbonate effluent. Sodium bicarbonate is then isolated through a filtering process.
Sodium bicarbonate can also be mined, primarily from two naturally occurring compounds: Trona and Nahcolite, and both minerals are abundant in the USA, Turkey, Botswana, and Kenya. Trona is a sodium carbonate compound that can be used to produce sodium bicarbonate, and Nahcolite is a natural mineral that has an identical composition to sodium hydrogen carbonate. Natural deposits of Trona and Nahcolite require further processing to be used for exhaust gas cleaning.
100% SOx absorption rates can be achieved depending on:
SodaFlexx creates a bespoke solution by incorporating these factors to maximise the SOx absorption rates, ensuring that the greatest efficiency is attained.
The initial step in the absorption process is the thermal decomposition of the sodium bicarbonate to produce sodium carbonate, carbon dioxide, and water. The initial temperature at which this decomposition occurs is 80°C, which is easily achieved in the exhaust gas stream of a marine engine or boiler.
2NaHCO3 → Na2CO3 + CO2 + H2O
This reaction is crucial for SOx abatement as the product yielded from this decomposition – sodium carbonate – in turn reacts with sulphur oxides producing sodium sulphate and sulphite. Sodium carbonate is strongly alkaline in nature, and when combined with acidic flue gas, it produces a neutral sodium salt (pH 7) and carbon dioxide. The two reactions are as follows:
Na2CO3 + SO2 → Na2SO3 + CO2
Na2CO3 + SO3 → Na2SO4 + CO2
The non-toxic salts are collected in a proprietary filter system and treated for safe disposal.
During the combustion process, sulphur is oxidised into sulphur oxides (SOx) which is a collective term for sulphur dioxide (SO2) and sulphur trioxide (SO3). The major constituent is sulphur dioxide, and sulphur trioxide forms to a much lesser extent (1-3% of SOx in boilers and 2-5% of SOx in engines). Sodium sulphite is formed, however, the sulphite is further oxidised by free oxygen present in the flue exhaust gas, so the main salt produced is sodium sulphate.
2Na2SO3 + O2 → 2Na2SO4
Naturally, sodium bicarbonate is hygroscopic and soluble in water. If mixed with water, carbonic acid forms which readily decomposes to carbon dioxide. Carbonic acid is not hazardous but, can possibly cause minor degradation of the bicarbonate product. This may lead to less efficient reactant but, with the addition of a propriety additive, SodaFlexx bicarbonate repels moisture. This increases the stability of the product in storage, reducing its tendency to ‘cake.’
Bicarbonate is subjected to ‘caking’ through exposure to non-ideal conditions of excess heat (60°C) or moisture (relative humidity in excess of 70%). SodaFlexx storage systems employ a dry air blanket and other measures to mitigate caking. The blanket prevents the sodium bicarbonate from picking up additional moisture in storage, and an anti-caking agent which induces the hydrophobicity and maintains the free-flow properties of the product.
Sodium sulphate is a neutral salt with a pH of 7 in aqueous solutions. During the absorption reaction, the pH shifts from acidic to alkaline conditions (exhaust systems are built to withstand a pH of 1-3). As the milled particles are very small (20 microns), they will not accumulate in the flue gas, so no corrosion.
Sulphate-induced hot corrosion happens due to alkaline sulphate deposits damaging components in the exhaust system – there are two types. Type I initiates between 800-950°C, the bicarbonate is injected at much lower temperatures downstream and so it does not apply for SodaFlexx. Type II occurs when there is a sufficient SO3 supply, which further reacts with the sodium sulphate. SO3 is minimal and present at the end of the flue and so both types of corrosion are extremely unlikely.
The ideal residence time for the reaction is 1-2 seconds. Sodium bicarbonate is injected into the exhaust stream directly after the turbocharger, and the reaction commences immediately. The reaction is positively affected by higher temperatures, and as the temperature rises so does the reaction rate. Typical exhaust gas temperatures post the turbocharger are within a range of 225°C to 245°C, which provides optimal temperature conditions for this reaction.
Unprocessed sodium bicarbonate is not the optimal particle size for the absorption process, as there is not enough active surface area for sufficient SOx removal. SodaFlexx provides absorbent that is milled to the ideal specification that increases the active surface area and increases SOx absorption.
Bureau Veritas, RINA, Lloyds Register. Other IACS classification societies will approve.
90 % < 30 µm, 100 % < 100 µm
1. pH of the residual salt is always > 7 (alkaline) due to the presence of Na2CO3 2. At usual exhaust gas temperatures we will always be much above the dew point, so there won’t be liquid water in the gas => none out of more than 500 shore-based applications adds neutralizing agents.
Sodium bicarbonate is readily available around the globe. It can be mined, but this is expensive, CO2 intensive, and it does not yield consistent product. Unprocessed sodium bicarbonate is not the optimal particle size for the absorption process, as there is not enough active surface area for sufficient SOx removal. SodaFlexx provides absorbent that is milled to the ideal specification that increases the active surface area and increases SOx absorption. See MSDS of Solvair S350.
Vertical as proposed on the example drawing attached: – Diameter 2,500mm and height 13,000mm (both subject to detailed engineering. Alternatively, horizontal silos can be placed: – (LxWxH) 11,500 x 2,440, 3,000.
For the pneumatic transport from the truck into the silo on-board pressurized air, usually generated by the truck’s on-board compressor, is used.
Not hygroscopic, only soluble in water.
No. The SodaFlexx system uses a hot air blanket to regulate humidity and also air vibrators and fluidising beds to ensure maximum flowability.
NaHCO3 is a neutral, non-toxic and non-irritant product, also used in the food (“baking soda”), feed and pharmaceutical industry. MSDS will be shared.
No special storage restrictions.
There is no practical shelf life limitation. Under normal storage conditions (10 – 30°C, dry), NaHCO3 is chemically stable almost indefinitely. In a high humidity environment, some caking or crusting may occur, but this is remedied by the transfer screw of the dosing system.
We recommend changing the dust filters on an annual basis, and this should be about $1,000 and 30-60 minutes total.
The system will be delivered with two blowers for redundancy purposes. No critical spare parts are advised, we offer spare packages and long-term service agreement if desired.
During the production time of the system all pre engineering and preparations required to place the system on-board can be done. The estimated installation time is less than 3 days.
System delivery cost is estimated to be about €1.1 million. There is a possibility of a discussion of a quantity discount.
After installation has been done in port alongside the quay, one service engineer will sail with the vessel for one voyage for commissioning.
32 kW is installed and about 60% of this is used during operation. Therefore, the system uses about 19 kW.
After the reaction converts SOx to Na2SO4, approximately 80% of the initial injected powder remains. The amount of time to fill a 20ft tanktainer depends on the absorbent injection rate. For example, 1 mt of absorbent fully captured equals about 800 kg of sodium sulphate residue. No additional power requirements for this operation.