(Debug) In[]:=
Clear["Global`*"]​​ChlorineConsumedPerCPVCMass=.63​​ChlorineProducedPerEdenCreteMass=.71​​CPVCEnergyPerMass=Quantity[37.6,"Gigajoules"/"MetricTons"]​​EdenCreteEnergyPerMass=Quantity[3.5,"Gigajoules"/"MetricTons"]​​CPVCDensity=Quantity[1.56,"MetricTons"/"Meters"^3]​​EdenCreteDensity=Quantity[2.7,"MetricTons"/"Meters"^3]​​MaterialVolumePerLength=Quantity[231.886,"MetricTons"/"Meters"]/CPVCDensity+Quantity[545.908,"MetricTons"/"Meters"]/EdenCreteDensity​​EdenCreteVolumePerLength=EdenCreteMassPerLength/EdenCreteDensity​​CPVCVolumePerLength=CPVCMassPerLength/CPVCDensity​​Solve[{​​ChlorineMassProducedPerLength==ChlorineProducedPerEdenCreteMass*EdenCreteMassPerLength,​​ChlorineMassConsumedPerLength==ChlorineConsumedPerCPVCMass*CPVCMassPerLength,​​ChlorineMassProducedPerLength==ChlorineMassConsumedPerLength,​​MaterialVolumePerLength==EdenCreteVolumePerLength+CPVCVolumePerLength},{EdenCreteMassPerLength,CPVCMassPerLength},PositiveReals]
(Debug) Out[]=
0.63
(Debug) Out[]=
0.71
(Debug) Out[]=
37.6
GJ/t
(Debug) Out[]=
3.5
GJ/t
(Debug) Out[]=
1.56
t/
3
m
(Debug) Out[]=
2.7
t/
3
m
(Debug) Out[]=
350.833
2
m
(Debug) Out[]=
EdenCreteMassPerLength
0.37037
3
m
/t

(Debug) Out[]=
CPVCMassPerLength
0.641026
3
m
/t

Solve
:Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result.
(Debug) Out[]=
{}
(Debug) In[]:=
{}​​CPVCProducedPerEdenCreteMass=(1/ChlorineConsumedPerCPVCMass)/(1/ChlorineProducedPerEdenCreteMass)​​EdenCreteMassPerLength=Quantity[545.908,"MetricTons"/"Meters"]​​CPVCMassPerLength=CPVCProducedPerEdenCreteMass*EdenCreteMassPerLength​​EnergyPerLength=CPVCEnergyPerMass*CPVCMassPerLength+EdenCreteEnergyPerMass*EdenCreteMassPerLength​​LengthPerTime=EnergyPerLength/Quantity[500,"MegaWatts"]​​UnitConvert[LengthPerTime,"Days"/"Meters"]​​(20000/.57)/365
(Debug) Out[]=
{}
(Debug) Out[]=
1.12698
(Debug) Out[]=
545.908
t/m
(Debug) Out[]=
615.23
t/m
(Debug) Out[]=
25043.3
GJ/m
(Debug) Out[]=
50.0866
GJ/(mMW)
(Debug) Out[]=
0.579706
days/m
(Debug) Out[]=
96.1307