CERAMIC PROTECTION OF AN ATR INJECTION NOZZLE
Publication Date: 2008-Apr-14
The IP.com Prior Art Database
Ceramic protection of an ATR injection nozzle
1. The problem
The Auto Thermal Reforming process is a technology for producing hydrogen H2 and carbon monoxide CO that is widely used in the chemical and petrochemical industry. It is used to produce large quantities of synthesis gas by the combination of several chemical reactions. In ATR, methane is introduced in excess with oxygen O2 and steam, which is used in particular to cool the burner. A total exothermic combustion reaction takes place: CH4 + 2 O2 → 2 H2O + CO2.
The heat and gaseous products liberated by this reaction are used to initiate the following two other reactions:
- steam methane reforming reaction (SMR): CH4 + H2O → 3 H2 + CO,
- water gas reaction (WGS): CH4 + CO2 → 2 H2 + 2CO.
Due to the species present in ATR, the following reaction also takes place: CO + H2O → H2 + CO2
The gases in the burner have a pressure and a temperature of about 40 bar and 1000°C.
Figure 1: The ATR process
Problems of degradation of the ATR burner are encountered at the plant. Over time, the material of the tip of the ATR burner is stripped off. This degradation demands the shutdown of the process and the replacement of the defective burner. This shutdown causes a considerable loss of income because the process is normally continuous.
The degradation of the ATR injection nozzle is caused by chemical attack (oxidation: CH4-O2 mixture) and thermal attack (thermal shock at startup, adhesion of the flame to the burner, local temperature probably higher than 1200°C).
Figure 2: ATR injection nozzle
2. Proposed solution
2.1 Ceramic protection
One solution is to protect the metal part by a thin (300mm) ceramic coating.
The ceramic coating must meet the following requirements:
- stability at high temperature in oxidizing, or even locally reducing, environment,
- TEC very close to that of the metal alloy,
- in case of deposition, chemical compatibility with the metal alloy (generally presence of common chemical elements),
- resistance to thermal shocks mainly during startup.
After analysing various ceramic coatings, yttriated zirconia was selected.
The ceramic deposit acts as a thermal and chemical barrier. Due to its low thermal conductivity coefficient, it causes the temperature to decrease significantly. Thus, the hot side of the metal is no longer directly exposed to a high temperature (provided the cold side is cooled). The proposed deposit is yttriated zirconia (YSZ: ZrO2 –Y2O3 at 7‑8% by vol). An NiCrAlY bonding undercoat is first deposited on the metal part. An intermediate gradient is also provided (NiCrAlY x vol % – YSZ y vol % coat).
2.2 Deposition methods
The ceramic coating can be deposited on the part to be coated using various processes mostly belonging to two distinct families:
· coatings s...