Two MECS case studies on VectorWall and HexWall furnace internals: lower NOx at higher output, and a furnace lifted in whole.
More acid, less NOx, the same furnace shell.
The baffle walls decided whether that was possible.
This paper by MECS, presented at Sulphur 2015, shows how ceramic furnace internals change what a sulfuric acid furnace can do. In a spent acid plant, staged combustion with oxygen enrichment and a VectorWall reached the NOx target at higher production in the existing furnace. In a second plant, HexWall baffles made it possible to brick a new furnace before the shutdown and lift it into place.
Figures from the MECS paper, spent acid regeneration and sulfuric acid plants, 2013 to 2015.
Most of a sulfuric acid plant is fixed once it is built, but the flow inside the furnace can be redesigned within one turnaround.
In 2015 a spent sulfuric acid facility wanted more capacity and lower stack NOx. Before the revamp, NOx was 120 to 150 mg/Nm³ at 900 tons of acid per day. The target was 100 mg/Nm³ at 1,076 tons per day.
MECS recommended staged combustion with oxygen enrichment. A second furnace was ruled out by footprint and budget, so the staging had to happen inside the existing one. Combustion and CFD modeling showed that a partially blocked first wall forces the staged air down into the gas, and that vector tiles on the lower part of the wall create the mixing vortex.
The plant reached its production and emissions goals, and the field data confirmed the model. The paper uses the VectorWall mixing checkerwall as the key part of the design.
In late 2013 a sulfuric acid plant replaced a furnace of 1.1 million pounds. To fit the turnaround, the new furnace was fully bricked before the shutdown and lifted into place. Brick and mortar baffles crack and their stability depends on the installer, so the owner used HexWall checkerwall blocks, keyed into the lining and stacked without mortar. They survived the lift, and they went in at about one third of the time a brick baffle wall would have taken.
The paper compares three brick baffle walls with one VectorWall in a sulfur burning furnace. The single wall gives a lower pressure drop and a narrower residence time distribution, so more of the gas spends close to the design time in the furnace. The authors conclude that new furnaces can be built smaller, and show capital savings for a 10% smaller furnace in a table that is not reproduced here.
If you plan a debottleneck or face a tighter NOx limit, the furnace internals belong in the first study, together with burner and air staging. The spent acid regeneration page explains where the walls sit in that furnace, and Unique Furnace Challenges adds a later MECS article on sulfur burning furnaces.
MECS sells these internals for sulfuric acid service as MECS VectorWall and MECS HexWall.
Both. CFD and combustion modeling set the wall configuration, and the plant then met its production and emissions goals in operation.
The blocks are fully supported on all six faces and keyed into the lining, so the wall holds its shape when the furnace moves.
In the sulfur burning furnace the paper models, yes, with lower pressure drop and a narrower residence time distribution.
MECS, which offers them as MECS VectorWall and MECS HexWall furnace internals made by Blasch.
Tell us the furnace type, the diameter and the NOx or capacity target. A Blasch engineer works with your licensor on the wall design.
