Methane Steam Reformer Re-Tube Evaluation

Methane Steam Reformer Re-Tube Evaluation By Gerard B. Hawkins Managing Direct or, CEO Contents    Design m et hodology applied • Mechanical design • Process design Case st udies Why work wit h GBHE ? Introduction   The t ubes in a prim ary reform er are a key consum able Different t o t he m aj orit y of hardware on a synt hesis gas plant  They have a lim it ed life  They fail due t o creep dam age Design Methodology   Underst and present operat ion Base Case - sim ulat e exist ing reform er • At norm al condit ions • Using exist ing t ube design • Det erm ines t he required m inim um perform ance for all ot her cases • Det erm ines t he base line life for all ot her cases Design Methodology      Then select a t ube m at erial t o use • Always go for an im proved m et allurgy Select a cat alyst t ype t o give required benefit s • I nit ial select exist ing cat alyst but ‘like for like’ cat alyst change m ay not be opt im al • Look at effect of large m at rix cat alyst and change size Sim ulat e re- t ube case Det erm ine pressure and t em perat ure profile Det erm ine st ress ( σ) and use Larsen- Miller plot t o det erm ine design t em perat ure Design Methodology      Must be careful wit h st ress dat a Som e t est s have been conduct ed over a short period of t im e • May not be represent at ive GBHE has reviewed m anufact urers st ress dat a and elim inat ed any dubious dat a There is st ill a large degree of variat ion Therefore use a percent age of t he average st ress dat a Design Methodology Stress Average Reported Stress Design Curve 80% of Average Reported Stress Temperature Design Methodology    Deduct off a m argin t o give Maxim um Allowable Operat ing Tem perat ure ( MAOT) Check if MAOT is great er t han m axim um predict ed t em perat ure I ncrease/ decrease t ube wall t hickness if required Typical Options        Typical t o upgrade t o a m odified m icro- alloy Such as H39WM, XM or KHR35CT Use m inim um sound wall t hickness of 8 m m Keep out side diam et er const ant Allow inside diam et er t o be increased Can inst all sm aller cat alyst and keep pressure drop below t hat of base case Or inst all a larger pellet and generat e large pressure drop benefit s Typical Tube Compositions HK40 IN519 36X H39W H39WM XM Alloy HK40 20% Ni Alloy IN519 24% Ni Manaurite 36X (Pompey) Alloy H39W (APV) Paralloy H39WM Manaurite XM 25% 24% 33% 33% 35% 33% Cr Cr 1% Nb Ni 25% Cr 1% Ni 25% Cr 1% Ni 25% Cr 1% Ni 25% Cr 1% Nb Nb Nb + Ti Nb + Ti Relative Allowable Stresses 200 HK40 100 IN519 50 H39W 20 36X 10 XM 5 2 700 740 780 820 860 900 940 980 720 760 800 840 880 920 960 1000 Temperature °C Typical Tube Upgrades   I f using HK40 or sim ilar • Replace wit h HP or HP Mod • Can get a large change in perform ance due t o large reduct ions in t ube wall t hickness I f using HP • Replace wit h HP Mod • Can get sm aller changes in perform ance since t he reduct ion in t ube t hickness is sm aller Options for Catalyst Optimization   A re- t ube can allow for an opt im izat ion of t he cat alyst loading since t he t ube I D can be increased I f t ube wall t em perat ure are lim it ing • Re- t ube will reduce peak t ube wall t em perat ures since t here is m ore cat alyst and hence m ore react ion • Can inst all a sm aller shape - no increase in pressure drop Options for Catalyst Optimization    Pressure drop will be reduced • Can reduce even furt her by inst alling larger cat alyst m at rix • Allows plant rat e increases Reduce flue gas t em perat ure • Allows for plant rat e increases • Rem ove coil skin t em perat ure lim it at ions Reduced ATE • Reduces m et hane slip Example - Ammonia Plant  By opt im izing bot h t he t ube I D and cat alyst com binat ion, achieved, • Reduct ion in ATE • Reduced pressure drop by 60% • Reduced m axim um t ube wall t em perat ures by 40°C • I ncrease radiant box efficiency • And can increase t hrough put by 3% Example - Methanol Plant Name Tube material Plate Rate Wall Thickness Methane Slip Exit Temperature Approach to Equilibrium Pressure Drop Maximum Tube Temperature Fluegas Temperature Savings Units n/a % mm mol % °C °C bara °C °C US$/yr Case 1 HK40 100 13.5 2.80 869 7.3 5.2 921 1126 n/a Case 2 Microalloy 100 13.5 2.80 869 7.3 5.2 921 1127 n/a Case 3 Microalloy 115 8 2.80 869 5.5 3.4 910 1113 1,000,000 Case 4 Microalloy 105 8 2.2 869 5.6 3.44 925 1125 340,000 Example - Methanol Plant     Can reduce ATE and hence m et hane slip I ncrease product ion t o realise bet ween 5 and 15% ext ra capacit y wort h US$330,000- 1,000,000 per year Reduce pressure drop by 1/ 3 rd I ncrease radiant reform er efficiency Why Work with GBHE ?     GBHE has operat ing experience of st eam reform ers GBHE has design experience of st eam reform ers and in part icular re- t ubes GBHE underst ands t he problem s and issues associat ed wit h re- t ubes This m eans t hat GBHE is in a unique posit ion t o help wit h reform er re- t ubes Why Work with GBHE ?  This m odel include rigorous m odelling of • Heat t ransfer on fluegas and process gas side • Kinet ic m odels for • Carbon predict ion • Pressure drop • Full t ube st ress Details of VULCAN REFORMER SIMULATION   Also includes effect of • Process condit ions changes on t ube life • Coffins • Tunnel port effect s • Napht ha feeds This m eans t hat VULCAN REFORMER SI MULATI ON is becom ing a leading prim ary reform er sim ulat ion package Other Issues    I f t he re- t ube allows for a plant rat e increase t hen m ust consider ot her part s of t he plant Fluegas rat e will increase • Can t he fluegas duct coils cope wit h t he increased dut y ? Process gas rat e t hrough t he reform ed gas cooling t rain will rise • Can t he reform ed gas cooling t rain cope ? Other Issues     What will t he effect be on t he downst ream cat alyt ic unit s ? • For exam ple - HTS/ LTS What will happen t o plant product ion GBHE has m odels t o perform t his analysis Can sim ulat e all unit operat ions in det ail and det erm ine perform ance post re- t ube Middle Eastern Ammonia Plant      During discussions re- t ube was m ent ioned Conduct ed 3 phase approach Process design - US$ 10,000 : 1 days work Fluegas m odelling - US$ 20,000 : 10 days work Det ailed t ube design - US$ 75,000 • Perform ed by a Engineering Cont ract or Conclusions      GBHE has an un- paralleled experience is design and operat ion of st eam reform ers GBHE has proj ect m anagem ent experience of re- t ubes GBHE can det erm ine t he effect of a revam p using t he world leading VULCAN REFORMER SI MULATI ON sim ulat ion m odel. GBHE can opt im ize t he cat alyst loading using t he world leading large m at rix cat alyst GBHE can det erm ine effect of re- t ube on downst ream and associat ed unit operat ions