Internals, Design & Manufacturing | DAIER Chemical Separation Standard

Engineering Reference for Process Engineers

 

Section 6: Internal Components (Distributors, Support Plates, Redistributors)

31. Q: What are the types of liquid distributors and their selection criteria?A: (1) Trough-type distributor – for high flow rates, good turndown. (2) Orifice pan distributor – for clean services, moderate flow. (3) Spray nozzle distributor – for low flow, but prone to fouling. Selection based on liquid flow rate, turndown ratio, fouling tendency, and required distribution quality.

32. Q: How many drip points per unit area are required for a liquid distributor?A: For random packing: 20-50 drip points per m² of column cross-section. For structured packing: 50-100 points per m². Higher point density improves distribution but increases cost. For very large columns (>3 m diameter), 100-200 points per m² may be specified.

33. Q: What is the function of a liquid redistributor and when is it needed?A: A redistributor collects liquid from the packing above and re-distributes it uniformly to the packing below. Needed when bed height exceeds 5-6 meters for random packing or 8-10 meters for structured packing. Also used when column diameter is large (>1.5 m) to correct wall flow.

34. Q: What are the requirements for packing support plates?A: Support plates must: (a) hold the packing weight without excessive deflection, (b) allow free gas and liquid passage, (c) prevent packing from falling through. Open area should be >50% of column cross-section. Common types: grid-type, beam-type, and gas-injection type.

35. Q: What is a bed limiter and when is it used?A: A bed limiter is a grid placed on top of the packing bed to prevent fluidization or expansion due to high gas flow. Required when gas velocity exceeds 70% of flooding or for light packing (plastic). Also used to hold packing in place during pressure surges.

Section 7: Design and Sizing Methodology

36. Q: What are the steps to design a packed column?A: (1) Define separation duty (theoretical stages). (2) Select packing type and material based on process conditions (corrosion, temperature, fouling). (3) Calculate column diameter from hydraulic capacity (flooding velocity, turndown). (4) Calculate packed height from HETP or transfer unit method. (5) Design internals (distributor, support, redistributor). (6) Specify installation details.

37. Q: How is packed height calculated using HETP?A: Packed height = (number of theoretical stages) × HETP. Example: 10 stages required, HETP = 0.5 m → height = 5 m. For random packing, HETP depends on packing size and system properties. For structured packing, HETP is often correlated with F-factor.

38. Q: How is packed height calculated using the transfer unit method?A: For absorption and stripping: Height = NTU × HTU, where NTU = number of transfer units (integral of dY/(Y-Y*)), HTU = height of a transfer unit = G/(K_G·a·ρ). HTU is typically 0.3–1.0 m.

39. Q: How is column diameter determined?A: Diameter is calculated from the required gas velocity, typically 50-80% of flooding velocity. Use the GPDC or flooding correlation to find flooding velocity u_flood. Then operating velocity u = 0.5–0.8 × u_flood. Column cross-section area = gas flow rate / u.

40. Q: What turndown ratio can be expected?A: Turndown ratio is the range of operation from minimum to maximum flow. Typical values: random packing 3:1 to 5:1; structured packing with high-performance distributor 4:1 to 6:1; poorly designed systems may be <2:1.

Section 8: Manufacturing, Quality, and Testing41. Q: How is metal packing manufactured?A: Metal packing is made from sheet metal (0.2–1.0 mm thickness) by stamping, punching, and forming. Pall rings: sheet is slit, windows punched, then rolled into cylinder. Structured packing: corrugated sheets are formed and assembled into modules.

42. Q: How is ceramic packing manufactured?A: Ceramic packing is formed by extrusion or pressing of clay mixtures, dried, then fired at 1200-1400°C. Quality control includes dimensional check, crush strength test, thermal shock resistance, and chemical analysis (alumina/silica content). Porosity measured by water absorption.

43. Q: What quality standards apply to tower packing?A: ISO 9001 for quality management system. Material certifications: EN 10204 3.1 for metals, ASTM standards for specific alloys. Dimensional tolerances: typically ±3-5% of nominal size. For structured packing, corrugation angle tolerance ±1°.

44. Q: What is a factory acceptance test (FAT) for structured packing?A: FAT includes visual inspection of corrugation uniformity, measurement of specific surface area (by geometric calculation), pressure drop test on a sample module, and material verification (PMI). Documentation includes test certificates.

45. Q: How is packing surface area verified?A: For random packing, specific surface area is calculated from geometry using CAD models. For structured packing, it is calculated from sheet dimensions, corrugation pitch, and angle. Third-party verification can be done by measuring a representative sample.

👉Need distributor drawing or quality docs?