Temperature Industrial Process Heating ------Progress Dan Zhou - - PowerPoint PPT Presentation

Thermal Energy Storage for Medium Temperature Industrial Process Heating

Dan Zhou

CREST Loughborough University

• -----Progress

Progress

• Materials Update
• System Update
• System Performance

Materials

Salt Price (per Metric Ton) Ca(NO3)2 $250 ~ $280 NaNO3 $300 ~ $500 KNO3 $700 ~ $900 LiNO3 Around $10,000 NaNO2 $400 ~ $500 NaCl $50 ~ $100 ZnCl2 $950 ~ $1000 KCl $500 ~ $900 Na2CO3 $180 ~ $250 Sr(NO3)2 Around $3,000 NaOH $350 ~ $450

PCMs Melting temperature (°C) Latent heat (kJ/kg) Price ($/kg) ZnCl2 - NaCl - KCl 203 NaOH - Na2CO3 210 KNO3 (54wt%) - NaNO3 (46wt%) 222 161 ~0.62 NaNO3 - NaNO2 226-233 Ca(NO3)2 (45wt%) - NaNO3 (55wt%) 230 ~110 ~0.33 Ca(NO3)2 - NaNO2 200-223 Ca(NO3)2 - LiNO3 235 LiNO3(12wt%) - NaNO3(18wt%) - KNO3(70wt%) 200 ~1.84 LiNO3(57wt%) - NaNO3(43wt%) 193 248 ~5.8 LiNO3(49wt%) - NaNO3(51wt%) 194 265 ~5.1 LiNO3(87wt%) - NaCl(13wt%) 208 360 ~8.7 LiNO3(45wt%) - NaNO3(47wt%) - Sr(NO3)2(8wt%) 200 199 ~4.9 Table 1 Potential molten salt mixture as medium temperature heat storage media Table 2 Market prices of some salts

Material investigations contain two parts:

• 1. Research stage

1) Binary system with lithium nitrate 2) Ternary system of LiNO3(12wt%) - NaNO3(18wt%) - KNO3(70wt%)

• 2. Industrial application stage

1) KNO3 (54wt%) - NaNO3 (46wt%) 2) Ca(NO3)2 (45wt%) - NaNO3 (55wt%) 3) Ternary system of LiNO3(12wt%) - NaNO3(18wt%) - KNO3(70wt%) 4) Other new ternary or quaternary systems

Binary system with lithium nitrate (Research stage)

• LiNO3(87wt%)- NaCl(13wt%)
• LiNO3(57wt%)-NaNO3(43wt%)
• Ca(NO3)2-LiNO3 (To be test….)

Heat storage system

Double pipes heat exchanger: heat transfer pipe can be smoothed pipe or enhanced pipes Outside pipe diameter Do: 50 mm Inside pipe diameter Din: 20 mm Pipe length: 1 m

Helical coiled tube

Heat storage system

• High temperature oil pump

(Turbine pump)

• M pumps CM MAG-M series

magnetically coupled centrifugal

• pump. Differential head: 6m;

capacity: 2-15 L/min; working temperature: up to 300°C .

• IC-LPM industrial paddle wheel

series flow meter:

• 2-20L/min
• Operating temperature: 350 °C
• High temperature heat

exchanger: Exergy tube –in-tube heat exchanger ½’’ NPT male inner tube connections and 1’’ NPT female outer tube boss.

• Highly dynamic

temperature control system: Julabo

U-value calculation

• 1. Mass of the PCM

(1) Cross area: (A) Pipe 1: 𝐵1 = 𝜌(

𝐸𝑃 2 )2= 1.96 × 10−3𝑛2 ; Pipe 2: 𝐵2 = 𝜌( 𝐸𝑗𝑜 2 )2= 3.14 × 10−4𝑛2

(2) Volume of the PCM (VP) 𝑾𝑸 = 𝐵1 − 𝐵2 𝑴 = 1.646 × 10−3𝑛3 (3) Mass of the PCM (MP) 𝑵𝑸 = 𝝇𝑸 ∙ 𝑾𝑸 = 𝟑𝟒𝟔𝟔 × 1.646 × 10−3𝒍𝒉 = 3.88𝒍𝒉 (4) Suppose the latent heat of the PCM 𝑰𝑸=

300𝒍𝑲 𝒍𝒉 ; total latent heat: 𝑴𝒊𝒇𝒃𝒖 = 𝑵𝑸 ∙ 𝑰𝑸= 3.88 × 300 𝒍𝑲 = 1162.9 𝒍𝑲

• 2. Suppose the flow rate inside the heat transfer tube is 𝒘𝒈 = 𝟏. 𝟔𝒏/𝒕

(1) The volume flow rate (𝒘 𝒈) 𝒘 𝒈 = 𝑩𝟑 ∙ 𝒘𝒈 = 3.14 × 10−4 ×

0.𝟔𝒏𝟒 𝒕

= 𝟐. 𝟔𝟖 × 𝟐𝟏−𝟓𝒏𝟒/𝒕 (2) The mass flow rate (𝒏 𝒈) 𝒏 𝒈 = 𝒘 𝒈 ∙ 𝝇𝒈 = 𝟐. 𝟔𝟖 × 𝟐𝟏−𝟓 ×

𝟖𝟓𝟕𝒍𝒉 𝒕

= 𝟏. 𝟐𝟐𝟖𝒍𝒉/𝒕 (3) Reynolds number at T=250°C 𝑆𝑓 =

𝒘𝒈∙𝒆𝒋 𝜃𝑔 = 0.5×0.02 1.2×𝟐𝟏−𝟕 = 8333.333 So the flow is turbulent flow

(4) The Prantle number (Pr) 𝑄𝑠 =

𝜃𝑔∙𝐷𝑄𝑔∙𝜍𝑔 𝑙𝑔

=

1.2×𝟐𝟏−𝟕×2.72×713 0.118×𝟐𝟏−𝟒

= 19.722 (5) The Nusselt number 𝑂𝑣 = 0.023 × 𝑆𝑓0.8 × 𝑄𝑠0.4 = 0.023 × 8333.3330.8 × 19.7220.4 = 103.84 (6) The heat transfer inside the tube (ℎ𝑗) ℎ𝑗 =

𝑂𝑣𝑔×𝑙𝑔 Din

=

103.84×0.118 0.02

= 612.656 𝑋/𝑛2𝐿 (7) The minimum overall effective heat transfer coefficient estimation 𝑉 = 1 1 ℎ𝑗𝑑 + 𝜇𝑡 𝑙𝑡 + 𝜇𝑄 𝑙𝑄 = 1 1 612.656 + 0.001 19 + 0.015 0.7 = 43.3𝑋/𝑛2𝐿 Suppose the inlet temperature of the heat transfer oil is 300 °C The charging time is around 1 hour. The charging time can be shorten by enhanced pipes, such as finned pipe.

Performance calculation

Figure 1 Heat storage system performance

Figure 2 Influence of inlet temperature on the performance

Figure 4 Influence of effective heat transfer rate on the performance

Figure 3 Influence of heat transfer fluid velocity on the performance